Last updated: October 2026
By CalcOrigin Editorial Team
What the Calculator Covers
This page groups five common pours into separate calculators: rectangular slabs, square footings, and walls; holes, columns, and round footings; circular slabs and tubes; curb and gutter runs; and stairs. Each section has its own inputs and its own result panel, so a small job with a slab, three piers, and a curb can be priced without starting over for each shape.
Every length field carries its own unit selector. A plan that gives the slab in feet, the thickness in inches, and a column diameter in centimeters can be entered as written; the tool converts each value to a common unit before doing the arithmetic. Results appear in cubic feet, cubic yards, cubic meters, pounds, kilograms, and the number of 60 lb and 80 lb bags. The quantity field multiplies identical items, which is useful for a row of piers or several repeated footings.
What the page does not do is design the concrete. It does not choose reinforcement, check soil bearing, size forms, or confirm that a slab is thick enough for a loaded truck. Those decisions belong to a structural engineer, a building department, or the ready-mix supplier who knows the local code. The numbers here are a material takeoff, not a stamp of approval.
Start with a sketch and a tape measure. Write down each shape separately, note the unit you measured in, and enter the values into the matching section. The output is only as good as the dimensions behind it, so a few extra minutes with the tape usually saves more than a clever formula.
Slab Volume in Three Steps
A rectangular slab, footing, or wall is a box: volume equals length times width times thickness. The only trap is units. If the length and width are in feet, the thickness must also be in feet before multiplying, so a 6-inch slab becomes 0.5 foot. Multiply the three numbers and the answer is in cubic feet.
Take a driveway 20 feet long, 12 feet wide, and 6 inches thick. In feet the thickness is 6 ÷ 12 = 0.5. The volume is 20 × 12 × 0.5 = 120 cubic feet. Divide by 27 to convert to cubic yards: 120 ÷ 27 = 4.44 cubic yards. At 150 pounds per cubic foot, that pour weighs about 18,000 pounds, or 9 short tons.
For a 4 × 8 foot patio at 4 inches, the thickness is 0.333 foot and the volume is 10.67 cubic feet, or 0.40 cubic yard. A 10 × 10 foot slab at the same thickness comes to 33.3 cubic feet, or 1.23 cubic yards. Those are the numbers to compare with bag yields or a ready-mix order.
| Shape |
Formula |
Worked example |
| Rectangular slab, footing, or wall | L × W × H | 20 × 12 × 0.5 ft = 120 ft³ |
| Round column, pier, or hole | π × r² × H | 1 ft diameter × 10 ft = 7.85 ft³ |
| Tube or ring section | π × (R² − r²) × H | 3 ft outside, 2 ft inside, 8 ft = 31.4 ft³ |
| Curb and gutter | (curb depth × curb height + gutter width × flag thickness) × L | 100 ft section = 125 ft³ |
| Stairs | W × (N × run × rise ÷ 2 + platform depth × N × rise) | 4 ft wide, 10 steps = 50 ft³ |
Keep the working in the same unit family. Mixing inches into a feet-only multiplication is the most common source of a wildly wrong order, and the error usually shows up as a number that is 12 times too large or too small. A quick sanity check helps: a cubic yard is a cube about 3 feet on each side, so a small patio should be well under one yard, while a driveway is usually several yards.
Cement, Aggregate, and Water
Concrete is a mixture of cement, fine aggregate such as sand, coarse aggregate such as gravel or crushed stone, water, and often an admixture. Cement is the powder that reacts with water to bind the mix; it is not the same material as the finished concrete. A bag of cement alone will not make a strong slab, and a bag of concrete mix already contains cement and aggregates blended in roughly the right proportions.
A common site mix for general work is 1:2:3 by volume, meaning one part cement, two parts sand, and three parts coarse aggregate. A richer 1:1.5:3 mix is used where more strength or durability is wanted. The water-to-cement ratio is usually kept between about 0.45 and 0.55 by weight for normal structural concrete, and lower for severe exposure. These are starting points, not a mix design; aggregate grading, cement type, and curing all change the result.
| Mix by volume |
Typical use |
What to watch |
| 1:3:6 | Mass fill, subbase, nonstructural work | Low cement content; not for exposed structural concrete |
| 1:2:4 | General footings, walls, and thick sections | Workable but weaker than a richer mix at the same water content |
| 1:2:3 | Slabs, walkways, and driveways | A common general-purpose blend when placed and cured well |
| 1:1.5:3 | Structural elements and higher-strength work | More cement and more heat; supplier should confirm the design |
Water is the variable most often abused. Adding a splash to make the mix flow raises the water-to-cement ratio and lowers strength, even though the concrete looks easier to place. If a mix is too stiff, a plasticizer or a different supplier mix is a better answer than a hose. The same principle applies to bagged concrete: mix to the water quantity on the bag, not to a consistency that feels comfortable.
Admixtures can accelerate set in cold weather, retard it in heat, entrain air for freeze-thaw resistance, or improve workability without extra water. They are not a substitute for good proportioning. For anything larger than a small flatwork pour, ask the ready-mix supplier to recommend a mix by exposure and strength rather than ordering a generic blend.
Weight, Density, and Truckloads
Normal-weight concrete has a density of roughly 145 to 150 pounds per cubic foot, which is about 2,320 to 2,400 kilograms per cubic meter. This page uses 150 pounds per cubic foot, so one cubic yard weighs about 4,050 pounds, or roughly two short tons. A fully loaded ready-mix truck carrying 8 to 10 cubic yards is therefore moving 16 to 20 short tons of material before the truck itself is counted.
That weight matters beyond the invoice. It has to be carried by the subgrade, the forms, and any temporary access route. A truck that cannot reach the pour without crossing a septic field, a utility trench, or a lightweight bridge may need a pump or a shorter chute. The supplier usually asks about access before dispatch, and a failed delivery is expensive for everyone.
| Concrete type |
Density |
Metric equivalent |
Typical use |
| Lightweight | 90–120 lb/ft³ | 1,440–1,920 kg/m³ | Roof decks, insulating fills, reducing dead load |
| Normal weight | 145–150 lb/ft³ | 2,320–2,400 kg/m³ | Most slabs, footings, walls, and structural work |
| High density | 200 lb/ft³ and up | 3,200 kg/m³ and up | Radiation shielding and counterweights |
The weight shown by the calculator is the poured, cured concrete, including the water that was added on site. A pallet of dry bags weighs less than the concrete it produces, because the mix water adds mass. That is why a 4 × 8 foot patio can need 18 bags of 80 lb mix while the finished slab weighs about 1,600 pounds: the bags supply roughly 1,440 pounds of dry material, and the water makes up the difference.
Lightweight and high-density mixes change the arithmetic substantially. A roof deck specified with lightweight concrete may weigh two-thirds as much as normal concrete, which reduces the load on the structure. A shielding mix with heavy aggregate can weigh half again as much. If the project specifies either one, use the supplier's density rather than the default on this page.
Columns, Holes, and Footings
A round column, pier, or post hole is a cylinder, and its volume is π times the radius squared times the height. Use the radius, not the diameter: half of a 12-inch diameter is 6 inches, or 0.5 foot. A 12-inch column 10 feet tall therefore holds π × 0.5² × 10 = 7.85 cubic feet, or about 0.29 cubic yard. The calculator's second section takes the diameter directly and does the halving for you.
Footings are often a combination of shapes. A square pad under a round pier is a box plus a cylinder; a bell-bottom footing adds a third, wider cylinder at the base. Compute each part separately and add the volumes, or use the quantity field for a row of identical piers. It is better to overestimate a footing slightly than to discover halfway through a pour that the last form is short.
Embedded rebar, anchor bolts, and conduit displace a small amount of concrete. For ordinary residential work the difference is usually within the waste allowance, so it is not subtracted. On a heavily reinforced element the displaced volume can be a few percent, and the engineer's takeoff should be used instead of a simple geometric estimate.
Sono tubes and similar forms are sold by nominal diameter, and the actual inside diameter can differ slightly. Excavated holes are often wider than the form because digging a clean cylinder is difficult. If the hole is bell-shaped or the sides slough, the concrete volume can exceed the theoretical cylinder by a noticeable margin. Measure the hole, not just the tube, when the pour is going into an excavation.
Tubes and Ring Sections
A concrete tube, pipe, or ring footing is an annulus: a large circle with a smaller circle removed. Its volume is π times the difference between the outer radius squared and the inner radius squared, multiplied by the length. The result is the volume of the solid wall, not the empty space in the middle.
For a section with a 3-foot outside diameter, a 2-foot inside diameter, and an 8-foot length, the outer radius is 1.5 feet and the inner radius is 1 foot. The volume is π × (1.5² − 1²) × 8 = π × 1.25 × 8 = 31.42 cubic feet, or about 1.16 cubic yards. The wall thickness is 0.5 foot, or 6 inches, which is the difference between the radii.
Plans often give the outside diameter and the wall thickness instead of the inside diameter. In that case the inside diameter is the outside diameter minus twice the wall thickness. A 36-inch outside diameter with a 6-inch wall has a 24-inch inside diameter. Mixing up diameter and radius, or applying the wall thickness once instead of twice, produces a large error in the opposite direction.
A solid circular slab is a different calculation: π × radius squared × thickness, with no inner circle. The tube section assumes a hole through the middle, so using it for a solid pad will underestimate the concrete. Ring footings, manhole walls, and precast pipe sections are the usual candidates for the annular formula; a round patio is not.
Curb and Gutter Profiles
Curb and gutter is priced by the linear foot, but the concrete is ordered by volume, so the shape of the cross-section matters. The calculator treats the profile as two rectangles: the upright curb and the flat gutter pan. Their combined area is multiplied by the run length to get the volume.
The formula is (curb depth × curb height + gutter width × flag thickness) × length. Curb depth is the horizontal thickness of the curb section, curb height is its vertical rise, gutter width is the flat pan width, and flag thickness is the thickness of that pan. A 100-foot run with a 6-inch curb depth, 6-inch curb height, 2-foot gutter width, and 6-inch flag has a cross-section of (0.5 × 0.5) + (2 × 0.5) = 1.25 square feet. Multiply by 100 feet and the volume is 125 cubic feet, or 4.63 cubic yards.
Residential profiles are often smaller than arterial-road sections. Municipal standards may call for a 6- to 8-inch curb height, a wider gutter, or a thickened edge at the pavement joint. Transitions, driveway aprons, inlets, and radius sections break the run into pieces, so measure each straight segment separately and add them together.
Reinforcement, dowels, and joint details are not part of the volume calculation, but they affect labor and cost. A long curb pour also needs enough trucks or a continuous supply to avoid a cold joint at the end of the run. On a residential project the curb volume is usually small compared with the driveway or sidewalk, but the formwork and finishing can dominate the schedule.
Stairs and Landings
A solid stair is a stack of triangular prisms sitting on a base, plus a landing if the flight ends at a platform. Each step contributes a wedge with a volume of width × run × rise ÷ 2, and the platform contributes width × platform depth × total rise. Adding those parts gives a reasonable estimate for a filled stair.
For a flight 4 feet wide with 10 steps, a 12-inch run, a 6-inch rise, and a 2-foot platform, the step volume is 4 × (10 × 1 × 0.5 ÷ 2) = 10 cubic feet. The platform volume is 4 × 2 × (10 × 0.5) = 40 cubic feet. The total is 50 cubic feet, or about 1.85 cubic yards. The calculator's stair section applies the same geometry from the run, rise, width, platform depth, and number of steps.
That model assumes the steps are filled solid to the underside and that the landing is at the full height of the flight. A stair built over a sloped waist slab, a prefabricated pan stair, or a flight with open risers will use a different quantity. For those, the forming drawings or the stair fabricator's takeoff are more reliable than a simple prism estimate.
Stair dimensions are also regulated. The International Residential Code limits riser height and requires a minimum tread depth, and local amendments can be stricter. Check the code before building the forms, because changing the rise after the concrete is placed is not an option. Add 5 to 10 percent to the calculated volume for formwork irregularities and spillage, especially on a small monolithic pour.
Bags or Ready-Mix
Bagged concrete is sold by weight, but the number that matters is the volume each bag yields after mixing. A 60 lb bag yields about 0.45 cubic foot, and an 80 lb bag yields about 0.60 cubic foot. Those yields are typical for general-purpose concrete mix; a specialty mix may differ, so check the bag label before buying a pallet.
| Bag size |
Typical yield |
Bags per cubic yard |
Bags for a 4 × 8 ft slab at 4 in |
| 60 lb | 0.45 ft³ | 60 | 24 |
| 80 lb | 0.60 ft³ | 45 | 18 |
One cubic yard is 27 cubic feet, so it takes 45 bags of 80 lb mix or 60 bags of 60 lb mix to make a yard. A 4 × 8 foot patio at 4 inches is 10.67 cubic feet, which rounds up to 18 bags of 80 lb or 24 bags of 60 lb. A 10 × 10 foot slab at the same thickness is 33.3 cubic feet, or 56 bags of 80 lb and 75 bags of 60 lb after rounding up.
Bagged mix makes sense for small jobs where a truck cannot reach or the quantity is under about one cubic yard. Above that, the labor of mixing and wheelbarrowing dozens of bags usually costs more than ready-mix, and the quality is less consistent. Ready-mix also arrives at a specified strength and slump, which matters for a driveway or a structural element.
Suppliers often charge a short-load fee below a minimum quantity, and some sell in quarter-yard increments. Ask about the minimum, the delivery window, and whether a pump is needed before choosing between bags and a truck. A pallet of 80 lb bags weighs over 3,000 pounds, so plan how it will be moved from the delivery point to the work area; a pallet jack or forklift may be necessary.
What Makes Concrete Strong
Strength is mostly a story about water and cement. A lower water-to-cement ratio produces a denser paste and higher strength, while extra water increases porosity and reduces both strength and durability. The mix must still be workable enough to consolidate around reinforcement and fill the forms, which is why proportioning is a balance rather than a race to the lowest water content.
Compaction removes entrapped air, and curing keeps enough moisture in the concrete for cement hydration to continue. Moist curing for at least seven days is a common minimum for normal concrete; cold weather, blended cements, or a specification may require longer. Concrete typically reaches about 70 to 75 percent of its 28-day strength in the first week, which is why seven days is a useful milestone but not the end of the process.
| Application |
Typical 28-day strength |
Notes |
| Sidewalks, patios, and low-traffic flatwork | 2,500–3,500 psi | Air entrainment helps in freeze-thaw climates |
| Residential driveways and footings | 3,500–4,000 psi | Thickness and base preparation matter as much as strength |
| Structural slabs, beams, and columns | 4,000–5,000 psi | Designed by an engineer for the actual loads |
| Industrial floors and heavy-duty pavement | 4,500–6,000 psi | Often specified with fibers, reinforcement, or a special mix |
Temperature affects the rate of hardening. Hot weather can cause rapid set, plastic shrinkage, and a weaker surface if the concrete dries before curing begins; cold weather slows hydration and can leave the concrete vulnerable to freezing. Frozen ground under a slab is another problem, because thawing later removes support. Protect fresh concrete from freezing and avoid placing it on a frozen base.
Air-entraining admixtures create tiny bubbles that give water room to expand when it freezes, which improves freeze-thaw durability. Other admixtures adjust set time, workability, or permeability. They should be chosen for the exposure and the placement conditions, not added casually on site. For a driveway in a cold climate, an air-entrained mix placed at the right slump and cured properly will outperform a stronger but poorly cured mix.
Ordering Mistakes That Cost Money
The first mistake is ordering exactly the calculated volume. Forms bulge under the weight of wet concrete, excavation is rarely a perfect rectangle, and a slab thickness can vary by half an inch over a large area. Ordering 5 percent extra is reasonable for simple flatwork; 10 percent is safer for footings, stairs, and irregular shapes. A short load can mean a cold joint, a second delivery fee, and a weaker pour.
The second mistake is ordering too much. Concrete cannot be returned once it is mixed, and dumping the surplus is not free. A washout area has to be prepared, and some jurisdictions treat the residue as regulated waste. The waste allowance should be a deliberate percentage, not a guess that grows every time someone rounds up.
The third mistake is forgetting access and timing. A truck needs a firm route, room to turn, and a chute that can reach the forms. A pour that starts too late in the day may run into a delivery window or a plant cutoff. If the site is tight, a pump may be cheaper than a failed attempt to chute the concrete into place. Confirm the plan with the supplier before the day of the pour.
Finally, cutting or grinding cured concrete releases crystalline silica dust, which is a serious health hazard. Use wet methods, dust collection, and appropriate respiratory protection, and follow the OSHA silica standard for construction. A material estimate is not worth a lung injury; the safety controls belong in the plan from the start.
Measuring and Estimating Well
Measure each dimension more than once and at more than one point. A patio that is 12 feet wide at the house and 11 feet 9 inches at the far edge averages about 11 feet 10½ inches, and using the larger number adds unnecessary concrete. For an excavation, measure the bottom as well as the top, because sloped sides can add volume that a simple depth measurement misses.
| Application |
Typical slab thickness |
What else matters |
| Footpath or patio | 4 in | Compacted base and joint layout |
| Residential driveway | 5–6 in | Vehicle weight, subgrade, reinforcement |
| Garage floor | 5–6 in | Slope to the door and a vapor barrier |
| Commercial or heavy vehicle | 6–8 in | Engineer’s design and axle loads |
| Industrial floor | 8–12 in | Flatness, reinforcement, and joint details |
Break the work into simple shapes and keep a sketch with the dimensions beside each one. A foundation with a rectangular pad, a round pier, and a grade beam is three calculations, not one. The same approach works for a driveway with a widened apron or a walk that turns a corner: split it into rectangles, calculate each, and add the results.
Base preparation is not part of the concrete volume, but it affects how much concrete actually fills the form. A 4-inch slab over a soft spot may need a thicker section or a repaired base, and a form set on loose soil can settle or bow. Compact the base, set forms to the intended grade, and check the diagonal measurements to confirm the layout is square before ordering.
Keep a record of what was ordered and what was actually used. After a few jobs, the difference between estimate and delivery becomes a useful calibration for the next pour. The calculator gives a consistent starting point; the record tells you whether your measurements, waste allowance, or base conditions tend to run high or low.
Why Use This Calculator
The obvious benefit is avoiding arithmetic slips. Converting inches to feet, switching between cubic feet and cubic yards, and dividing by bag yields are all places where a decimal can move the wrong way. The tool performs the conversions consistently and shows the result in several units at once, which makes it easier to compare an estimate with a supplier's quote.
It is also fast enough to use as a what-if tool. Change the slab thickness from 4 to 5 inches and the volume changes by 25 percent; change the bag size and the bag count changes. Seeing those relationships before ordering is more useful than discovering them after the truck leaves. The page works on a phone at the job site and does not require an account.
The limits are worth stating plainly. The calculator does not design reinforcement, verify soil capacity, or replace a supplier's mix recommendation. It assumes simple geometric shapes and uniform thickness. A slab on a slope, a footing with a bell, or a stair with a curved landing may need to be split into smaller shapes or checked against the drawings.
For a broader takeoff, pair it with the volume calculator for non-concrete shapes, the gravel calculator for the base layer, and the square footage calculator for area. The combined numbers give a more complete picture of the materials and labor a project will need.
A Short Checklist
Sketch the work and label each shape. Measure length, width, and thickness in the units on the plan, then convert to a consistent unit before multiplying. Calculate repeated items with the quantity field, and add 5 to 10 percent for waste, over-excavation, and form deflection. Decide whether the volume is small enough for bags or large enough to justify a ready-mix truck.
Before ordering, confirm access, delivery time, and the supplier's minimum quantity. Check that the base is compacted, the forms are stable and square, and the reinforcement is in place with the specified cover. Have a washout area ready and a plan for finishing before the concrete arrives, because a pour is a deadline, not a rehearsal.
After the pour, cure the concrete and keep heavy loads off it until it has gained enough strength. The 28-day strength is the design reference, but foot traffic and form removal happen earlier under the supplier's or engineer's guidance. Record the actual quantity used so the next estimate is better.
The calculator is a practical estimating aid, not a substitute for local code, engineering judgment, or the supplier's advice. Used with careful measurements and a sensible waste allowance, it removes most of the arithmetic risk from a concrete order and leaves the important decisions where they belong.
Frequently Asked Questions
How much concrete do I need for a 10 × 10 ft slab?
At 4 inches thick, the volume is 10 × 10 × 0.333 = 33.3 cubic feet, or about 1.23 cubic yards. That is roughly 56 bags of 80 lb mix or 75 bags of 60 lb mix after rounding up. A thicker slab scales in direct proportion.
How many bags of concrete are in a cubic yard?
A cubic yard is 27 cubic feet. At 0.60 cubic foot per 80 lb bag, that is 45 bags; at 0.45 cubic foot per 60 lb bag, it is 60 bags. Actual yield varies slightly by mix, so check the bag label.
How much does a cubic yard of concrete weigh?
Normal-weight concrete at about 150 lb/ft³ weighs roughly 4,050 lb per cubic yard, or about two short tons. Lightweight mixes can be much lighter, and high-density shielding mixes can be considerably heavier.
How much extra concrete should I order?
Five percent is reasonable for a simple slab with accurate forms. Ten percent is safer for footings, stairs, irregular excavations, or a first pour. The extra covers form deflection, uneven subgrade, spillage, and small measurement errors.
What is the difference between cement and concrete?
Cement is the fine powder that reacts with water to bind the mix. Concrete is the finished material made from cement, sand, coarse aggregate, water, and sometimes admixtures. Cement is only one ingredient, typically a minority of the concrete by mass.
How long does concrete take to cure?
Concrete is usually designed for a 28-day strength, and it reaches most of that strength in the first four weeks. Moist curing for at least seven days is a common minimum. Curing continues slowly after 28 days, especially in thick sections.
What mix ratio should I use for a slab?
A 1:2:3 mix by volume is a common general-purpose starting point for slabs and walkways. A richer 1:1.5:3 mix is used for higher-strength work. Keep the water-to-cement ratio around 0.45 to 0.55 by weight unless the supplier specifies otherwise.
Can concrete be poured in cold weather?
Yes, with precautions. Do not place concrete on frozen ground, protect it from freezing, and keep it warm enough for hydration to proceed. Accelerators and insulating blankets may help. In hot weather, shade the materials, cool the mix, and start early to avoid rapid set.
How do I calculate concrete for a round column?
Use π × radius² × height. A 12-inch diameter column has a 6-inch radius, or 0.5 foot. At 10 feet tall, the volume is π × 0.25 × 10 = 7.85 cubic feet, or about 0.29 cubic yard.
How thick should a concrete slab be?
A footpath or patio is commonly 4 inches. A residential driveway or garage floor is usually 5 to 6 inches. Commercial driveways and heavy-vehicle areas often need 6 to 8 inches, and industrial floors are engineered for the loads. Local code and subgrade conditions can change these figures.
Which units does the calculator accept?
Each length field can be set to feet, inches, yards, meters, or centimeters. Results are shown in cubic feet, cubic yards, cubic meters, pounds, kilograms, and bag counts for 60 lb and 80 lb bags.
Can I use bagged concrete for a driveway?
Bagged mix is practical for small repairs and projects under about one cubic yard. A typical driveway needs several cubic yards, and mixing that many bags by hand is slow and inconsistent. Ready-mix is usually the better choice at that scale.
Does rebar reduce the amount of concrete I need?
Rebar displaces a small volume, but it is usually ignored in a residential takeoff because the difference falls within the waste allowance. On heavily reinforced elements, the engineer's takeoff or a small deduction may be appropriate.
What is a short-load fee?
A short-load fee is charged by some ready-mix suppliers when an order is below a minimum quantity, because the truck still has to travel and clean out. The threshold varies by supplier, so ask before ordering a small load.
