Enter a value, pick the unit you have, and pick the unit you want. The conversion covers metric, imperial, and a few specialist units such as carats and atomic mass units.
| Milky Way Galaxy | 1.15357 x 1042 kg or 5.8 x 1011 solar mass |
| Sun | 1.9891x1030 kg |
| Earth | 5.9736 x 1024 kg |
| Moon | 7.3477 x 1022 kg |
| Atomic Mass Unit (u) | 1.660539066(83) x 10-27 kg |
| Neutron | 1.67492729(28) x 10-27 kg or 1.0086649156(6) u |
| Proton | 1.672621637(83) x 10-27 kg or 1.00727646677(10) u |
| Electron | 9.10938215(45) x 10-31 kg or 5.4857990943(23)x10-4 u |
Long before anyone wrote down a definition of the kilogram, people needed a way to agree on how much of something they were handing over. The earliest standards were practical rather than scientific: a fixed number of seeds, a filled vessel, or a familiar stone. Because those objects were easy to carry and hard to fake, they became the reference points that merchants and tax collectors relied on.
Seeds left a lasting mark on the vocabulary of measurement. The carob seed gave us the carat, still used today for gemstones, and barleycorns became the basis of the old English grain and inch. A unit that could be counted out on a market stall was, for centuries, more useful than an abstract definition.
Mesopotamian scribes recorded a large unit called the talent, divided into sixty parts in keeping with their base-60 number system. Greek traders carried the idea westward, and Roman officials adapted it again. Rome's basic unit of mass was the libra, and its twelfth part was the uncia — the ancestor of both the English ounce and the inch. That habit of dividing by twelve survived long after the empire, which is why traditional weight systems are full of twelfths rather than tenths.
Medieval England juggled several competing pounds. The troy pound, used for precious metals, was divided into twelve ounces, and each ounce into twenty pennyweights; 240 of those pennies made up a pound sterling of silver. Trade in ordinary goods used a different standard, the avoirdupois pound of sixteen ounces, which eventually won out for everything except metals and medicines. A stone of fourteen pounds and a hundredweight of 112 pounds grew out of the same merchant arithmetic.
The British Weights and Measures Act of 1824 tried to impose order on this patchwork, defining the imperial gallon, bushel, and pound in law. A decade later, in 1834, fire destroyed the Houses of Parliament and with them the physical standards kept there, so a new set of national prototypes had to be made. Later legislation tightened the definitions further, and the imperial system travelled with British trade across the empire.
French scientists of the 1790s wanted something more rational. They tied length to the Earth and mass to water: the gram was defined as the mass of a cubic centimeter of water, which made the kilogram the mass of a liter. The system was adopted by revolutionary France, briefly rolled back under Napoleon, and then restored; the 1875 Treaty of the Metre gave it international standing, and a platinum-iridium cylinder kept near Paris served as the world's kilogram until 2019, when it was redefined in terms of the Planck constant.
What made the metric system spread was not politics but arithmetic. Every prefix is a power of ten, so converting between units means moving a decimal point instead of remembering that a pound holds sixteen ounces or a stone fourteen pounds. That single design choice is why most of the world now measures mass in grams and kilograms, and why scientists abandoned the older units almost entirely.
When a number in grams or kilograms is hard to picture, familiar objects help:
Although the terms weight and mass are often used interchangeably in everyday conversation, they have distinct scientific meanings. Understanding the difference is essential for accurate measurements and conversions.
Mass is the amount of matter in an object. It is a fundamental property that does not change regardless of location. An object with a mass of 10 kilograms on Earth will still have a mass of 10 kilograms on the Moon, in space, or anywhere else in the universe. Mass is measured in kilograms, grams, pounds-mass, and similar units. Our mass calculator can help with precise mass conversions.
Weight is the force exerted by gravity on an object's mass. Since gravity varies from place to place, weight is not constant. On Earth, the acceleration due to gravity is approximately 9.81 m/s², while on the Moon it is only 1.62 m/s². This means a person who weighs 180 pounds on Earth would weigh only about 30 pounds on the Moon, even though their mass has not changed.
In everyday life on Earth, weight and mass are proportional and the distinction is often unimportant. However, in scientific contexts, engineering, and space exploration, the difference is critical. Scales actually measure weight (the force), but are calibrated to display mass by assuming standard Earth gravity. This is why a spring scale gives different readings at the equator versus the poles, where gravity differs slightly. Our density calculator uses mass and volume to calculate density, which is independent of gravitational variations.
Converting between weight and mass units is straightforward once you know the conversion factors. Whether you are cooking, shipping packages, or working on scientific calculations, our weight converter makes the process simple. Understanding these conversions is essential in our interconnected world where different countries and industries use different measurement systems.
To convert pounds to kilograms, multiply by 0.45359237. For example, a 150-pound person weighs 150 × 0.45359237 = 68.04 kilograms. A 10-pound bag of potatoes weighs 4.54 kilograms. To convert ounces to grams, multiply by 28.3495. For instance, 8 ounces of cheese equals approximately 226.8 grams. These conversions are essential for international travel, medical dosages, and scientific research. If you also need to convert volume measurements, our volume calculator can help with related conversions between liters, gallons, and cubic meters.
To convert kilograms to pounds, multiply by 2.20462. For example, a 5-kilogram bag of flour weighs 5 × 2.20462 = 11.02 pounds. A 70-kilogram person weighs approximately 154.32 pounds. To convert grams to ounces, divide by 28.3495. For example, 500 grams of sugar equals about 17.64 ounces. These conversions are commonly used when following recipes, shipping goods internationally, or comparing product specifications. The precision of the conversion factor matters — using 2.2 instead of 2.20462 introduces a 0.2% error that can add up with larger numbers.
Metric conversions are simple because they are based on powers of ten. To convert from kilograms to grams, multiply by 1,000. To convert from grams to milligrams, multiply by 1,000. To convert from kilograms to metric tons, divide by 1,000. To convert from grams to micrograms, multiply by 1,000,000. The metric system's decimal nature makes it far easier to work with than imperial units for scientific and engineering applications. For example, converting 2.5 kilograms to milligrams is simply 2.5 × 1,000,000 = 2,500,000 milligrams — no complex fractions or memorized conversion factors needed.
Our weight calculator handles all these conversions automatically. Simply enter the value, select the source unit, select the target unit, and the result appears instantly. The calculator supports kilograms, grams, milligrams, tons, pounds, ounces, carats, atomic mass units, grains, US and UK quarters, and US and UK stones. This eliminates the need to memorize conversion factors and reduces the risk of calculation errors. For more complex calculations involving mass, volume, and density, try our density calculator which integrates these measurements seamlessly.
The two major systems for measuring weight and mass are the metric system and the imperial (US customary) system. Each has its advantages and is used in different parts of the world. Understanding both systems is essential for international communication, trade, and travel.
The metric system is used by over 95% of the world's population. Its base unit of mass is the kilogram, with prefixes like milli-, centi-, and kilo- indicating multiples of ten. The system was developed in France during the 18th century and is now the official system of measurement in most countries. One of the greatest advantages of the metric system is its consistency — converting between units simply requires moving the decimal point. For example, 1 kilogram = 1,000 grams = 1,000,000 milligrams. There is no need to memorize arbitrary conversion factors like 16 ounces per pound or 14 pounds per stone. The metric system's consistency makes it ideal for scientific work, international trade, and education. Our unit converter supports all metric prefixes and units for quick and accurate conversions.
The imperial system is primarily used in the United States and, to a lesser extent, in the United Kingdom and a few other countries. Its weight units include the pound (lb), ounce (oz), stone, and ton. The imperial system evolved over centuries from various historical measurement traditions, which is why its conversion factors are irregular. For example, there are 16 ounces in a pound, 14 pounds in a stone, and 2,000 pounds in a US ton. The UK (long) ton equals 2,240 pounds. These irregular conversions make the imperial system more challenging to work with, but it remains deeply ingrained in American culture, from body weight measured in pounds to food sold by the ounce. Many Americans have an intuitive understanding of pounds and ounces but find kilograms and grams unfamiliar.
The choice between systems depends on your location and field. If you are in the US, imperial units are standard for everyday use. For scientific work, international trade, and most professional fields, the metric system is preferred. Our weight calculator supports both systems, making it easy to convert between them regardless of which system you need. For professionals working in international contexts, being bilingual in both measurement systems is increasingly important. You may also find our density calculator useful when working with mass and volume measurements in either system, as it automatically handles unit conversions for you.
While there have been periodic efforts to convert the US to the metric system, change has been slow and expensive. The US officially adopted the metric system for trade and commerce in 1975 with the Metric Conversion Act, but the transition has been voluntary rather than mandatory. Today, many US industries use both systems — for example, soda is sold in 2-liter bottles (metric) while milk is sold in gallons (imperial). Understanding both systems and being able to convert between them remains an essential skill in our globalized world.
Weight and mass conversion is used in countless everyday situations. Understanding how to convert between units is a valuable skill in many fields, from professional environments to household tasks.
Recipes from different countries use different measurement systems. A European recipe might list ingredients in grams, while an American recipe uses cups and ounces. Accurate weight conversion ensures consistent results. For example, 250 grams of flour equals approximately 8.8 ounces. Professional bakers always use weight measurements for precision, as volume measurements can vary significantly depending on how ingredients are packed. A cup of flour can weigh anywhere from 120 to 150 grams depending on how it is scooped, while 120 grams is always 120 grams. This is why serious home bakers invest in a kitchen scale and learn to convert between ounces and grams.
Shipping companies charge based on package weight, and different countries use different units. International shipping requires converting between pounds and kilograms to calculate costs and meet regulatory requirements. A package weighing 22 pounds equals 10 kilograms, and knowing this conversion is essential for accurate shipping label preparation. Freight companies typically use kilograms for international shipments and pounds for domestic US shipments. Misunderstanding these units can lead to incorrect postage, delayed deliveries, or additional fees. Our weight calculator ensures you always use the correct values when preparing shipments.
Body weight is measured in pounds in the US and kilograms in most other countries. Fitness enthusiasts and travelers often need to convert between these units. Many fitness apps allow you to switch between units, but understanding the conversion helps you track progress regardless of the scale you use. A weight loss goal of 10 pounds is equivalent to 4.54 kilograms. Our BMI calculator accepts weight in both pounds and kilograms, making it accessible regardless of your preferred unit system.
Medical dosages are typically calculated in milligrams per kilogram of body weight, requiring precise conversion between units. Scientific research uses the metric system exclusively, but equipment from different sources may display measurements in different units, making conversion skills essential. Pharmacists regularly convert between grams, milligrams, and micrograms when preparing medications. Our mass calculator provides the precision needed for scientific and medical applications, and our unit converter supports all the units used in healthcare and laboratory settings.
Avoid these common errors when converting between weight and mass units to ensure accuracy in your calculations. Being aware of these pitfalls will help you get reliable results every time.
The most fundamental error is treating weight and mass as identical. While they are proportional on Earth, they are fundamentally different physical quantities. Mass is constant; weight varies with gravity. In most everyday contexts, the distinction is negligible, but in scientific and engineering work, it matters significantly. For example, a satellite's mass determines its orbital mechanics, while its weight is essentially zero in free fall. Always consider whether your application requires mass or weight, and choose the appropriate units and measurement method.
Many people use approximate conversion factors when exact ones are needed. For example, using 2.2 instead of 2.20462 for kilograms to pounds can introduce errors, especially with large numbers. For precise work, always use the exact conversion factors provided in our weight converter. A 0.2% error might seem small, but when converting 1,000 kilograms, the difference between 2,200 and 2,204.62 pounds is 4.62 pounds — enough to matter in shipping and manufacturing. Our unit converter uses precise conversion factors for all supported units to eliminate this potential source of error.
A US ton (2,000 pounds) is different from a UK ton (2,240 pounds). Similarly, US and UK quarts and gallons differ. When converting weights that involve these units, be sure to use the correct version. The difference of 240 pounds per ton can lead to significant errors in shipping and industrial applications. Our weight calculator clearly distinguishes between US and UK variants of units like quarters and tons, displaying both options so you can select the correct one for your needs.
When a calculation involves multiple measurements, ensure all are in the same unit system before proceeding. Mixing kilograms and pounds in a single calculation will produce incorrect results. This is especially common in recipes when some ingredients are measured in cups and others in grams, or in engineering when specifications from different countries use different units. Use our weight calculator to convert all values to a consistent unit before performing calculations with other tools like our density calculator or volume calculator, which assume consistent unit inputs.
Rounding intermediate results before the final calculation can introduce significant errors. Always keep full precision throughout your calculations and round only the final result to the appropriate number of significant figures. Our weight calculator handles this automatically, maintaining full precision internally and displaying results with appropriate formatting based on the magnitude of the value.
Follow these tips to ensure accurate weight and mass conversions every time, whether you are working in a professional laboratory or cooking in your home kitchen.
Familiarize yourself with the units you are converting between. Understand whether you are working with avoirdupois (standard) ounces or troy ounces, US or UK tons, and short or long hundredweights. Using the wrong variant can lead to significant errors. For example, a troy ounce (used for gold) is 31.1 grams, while a standard ounce is 28.35 grams — a difference of nearly 10%. When buying or selling precious metals, this distinction is critical.
For the most accurate results, use exact conversion factors rather than approximations. The exact conversion from pounds to kilograms is 0.45359237, not simply 0.45. Our weight converter uses precise factors for all supported units, ensuring reliable results down to the last decimal place. This level of precision is essential for pharmaceutical compounding, scientific research, and industrial quality control where small errors can have significant consequences.
When converting manually, verify your calculation by converting back to the original unit. For example, if you convert 10 pounds to kilograms, convert the result back to pounds to confirm accuracy. This simple check catches most conversion errors. Our weight calculator eliminates the need for manual verification because it performs all conversions with maximum precision and consistency.
The precision of your result should match the precision of your input. If you measure something as 5 pounds (one significant figure), reporting the result as 2.26796 kilograms implies more precision than you actually have. Round appropriately to avoid false precision. In general, your result should have no more significant figures than your least precise input measurement.
For professional or critical applications, always use a reliable conversion tool. Our weight calculator provides precise conversions across all common weight and mass units, from the largest (tons) to the smallest (atomic mass units). For related calculations, our density calculator and mass calculator use the same high-precision conversion factors and are designed to work seamlessly together for complex multi-step calculations.
Weight and mass conversion is a fundamental skill that applies to countless aspects of daily life, from cooking and shipping to science and medicine. Whether you are a student learning about measurement systems, a professional working with international standards, or someone who simply wants to follow a recipe from another country, understanding how to convert between weight units is essential.
Our free weight calculator simplifies the conversion process by supporting both imperial and metric units, including kilograms, pounds, ounces, grams, milligrams, tons, carats, and more specialized units like atomic mass units, grains, quarters, and stones. The calculator provides instant, accurate results with just a few clicks, eliminating the need to memorize conversion factors or perform manual calculations that are prone to error.
We encourage you to explore our other related tools to expand your measurement capabilities. Try our unit converter for all types of measurement conversions including length, temperature, area, and volume. Use our density calculator to explore the relationship between mass and volume, and our volume calculator for volume-related calculations. For health and fitness applications, our BMI calculator and body fat calculator both use weight inputs and support multiple unit systems, making them accessible whether you think in pounds or kilograms.
Understanding weight and mass conversions is more than just a practical skill — it is a window into the fascinating history of human civilization and trade. From ancient Babylonian talents to modern atomic mass units, the way we measure weight tells the story of our species' journey from local barter to global commerce. Bookmark this page and come back whenever you need to perform weight conversions. If you found this tool helpful, please share it with others who might benefit from quick and accurate weight and mass unit conversions. With practice, converting between pounds and kilograms will become second nature, saving you time and ensuring accuracy in all your measurement tasks.
Reference: the NIST Office of Weights and Measures publishes the official US definitions for customary units.
To convert pounds to kilograms, multiply the number of pounds by 0.45359237. For example, 10 pounds equals approximately 4.54 kilograms. Our weight calculator does this conversion instantly and supports both US and UK units.
There are 16 ounces in a pound (avoirdupois weight). This is part of the US customary system of measurement. The pound and ounce have been used for centuries in English-speaking countries.
A US quarter (quarter [US]) equals 25 pounds (or about 11.34 kg). A UK quarter (quarter [UK]) equals 28 pounds (or about 12.70 kg). The UK quarter is based on the imperial hundredweight of 112 pounds.
The stone is primarily used in the UK and Ireland to measure body weight. One stone equals 14 pounds (approximately 6.35 kg). It is commonly used when discussing personal weight in these countries.
One ounce (avoirdupois) equals approximately 28.35 grams. The troy ounce, used for precious metals like gold and silver, equals about 31.1 grams. Always check which ounce system you are using for accurate conversions.
Mass is the amount of matter in an object and remains constant regardless of location. Weight is the force exerted by gravity on that mass. On Earth, they are often used interchangeably, but on the Moon, your weight would be one-sixth of what it is on Earth while your mass stays the same.
To convert kilograms to pounds, multiply the number of kilograms by 2.20462. For example, 5 kilograms equals approximately 11.02 pounds. Our weight calculator can instantly convert between these and many other units.
A metric ton (tonne) equals 1,000 kilograms or approximately 2,204.62 pounds. It is the standard unit for measuring large masses in most countries. The short ton (US) equals 2,000 pounds, while the long ton (UK) equals 2,240 pounds.
There are 1,000 milligrams in a gram. The milligram is commonly used in medicine and pharmacology for precise dosage measurements. Our weight converter handles all metric prefixes automatically for accurate results.
A carat is a unit of mass used for gemstones and pearls, equal to 200 milligrams or 0.2 grams. The word carat comes from the carob seed, which was historically used as a standard for weighing precious stones.
To convert ounces to grams, multiply the number of ounces by 28.3495. For example, 8 ounces of flour equals approximately 226.8 grams. This conversion is essential in cooking when following recipes from different countries.
The US customary system, including pounds, originated from the British Imperial System. While most countries adopted the metric system for its simplicity, the US continues to use customary units due to historical precedent, infrastructure costs, and cultural familiarity with the existing system.