Weight Calculator
Weight Converter
Measuring weight (more precisely, mass) is one of the most fundamental and universal activities in everyday life, science, commerce, and engineering. Across the world, different systems of measurement have evolved. The metric system — used by most countries — defines mass in kilograms (kg), grams (g), and metric tons (t), while the imperial and US customary systems use pounds (lb), ounces (oz), and stones (st) for body weight.
The metric system is the official system of measurement in all but three countries (the United States, Myanmar, and Liberia), making it the global standard for science, medicine, and international trade. However, the US customary system remains deeply embedded in American daily life — road signs use miles, food labels show ounces and pounds, and body weight is measured in pounds.
This weight calculator solves the everyday problem of converting between these units instantly. Select your input unit, type a value, and instantly see the equivalent in grams, kilograms, metric tons, ounces, pounds, stones, and short tons (US).
The difference between mass and weight is a foundational concept in physics that many people encounter first through unit conversions. Mass is an intrinsic property of matter, measuring the amount of material in an object, and is constant regardless of location. Weight, by contrast, is the force exerted on that mass by gravity, calculated as mass times gravitational acceleration (W = mg). A person with a mass of 70 kg weighs approximately 686 newtons on Earth but only 114 newtons on the Moon — yet their mass remains 70 kg everywhere.
In everyday usage, the terms weight and mass are used interchangeably, and this calculator follows that convention. However, the distinction matters in scientific and engineering contexts. Physicists and engineers use kilograms for mass and newtons for weight-force. The pound-mass (lb) is the mass unit in the imperial system, while the pound-force (lbf) is the force unit. At Earth's surface, 1 lb-mass exerts approximately 1 lb-force of weight, which is why the distinction is rarely made in everyday conversation. This calculator converts mass units only and does not calculate weight-force in newtons.
- Choose the input unit from the dropdown menu — gram, kilogram, metric ton, ounce, pound, stone, or short ton.
- Enter the value you want to convert. Decimal values are supported.
- View all results simultaneously — the calculator displays the equivalent in every supported unit at once.
Choosing the Right Unit for Your Context: For most international scientific, medical, and commercial applications, kilograms and grams are the appropriate choice. For body weight in the United States, pounds are standard. In the United Kingdom and Ireland, body weight is traditionally expressed in stones and pounds (e.g., 11 stone 4 pounds). For cooking and baking, ounces and grams are both commonly used. For shipping and industrial materials, metric tons and short tons are the appropriate units. The calculator simultaneously displays all these options so you can choose the most suitable unit for your context.
Primary Conversion Factors
| 1 kg equals: | 1 lb equals: | |
|---|---|---|
| grams | 1,000 g | 453.592 g |
| pounds | 2.20462 lb | 1 lb |
| ounces | 35.274 oz | 16 oz |
| stones | 0.157473 st | 0.0714286 st |
| metric tons | 0.001 t | 0.000453592 t |
| short tons | 0.00110231 ton | 0.0005 ton |
Key Formulas
kg to lb: lb = kg x 2.20462. lb to kg: kg = lb x 0.453592. kg to st: st = kg x 0.157473. st to lb: lb = st x 14. kg to t: t = kg / 1000.
Mass vs. Weight
Mass (kg, lb) is the quantity of matter in an object. Weight-force (newtons) is the gravitational force acting on that mass: W = m x g. This calculator converts units of mass, not weight-force.
Mass Unit Comparison Table
| Unit | Symbol | Equals (kg) | Typical Use |
|---|---|---|---|
| Gram | g | 0.001 | Cooking, science, small items |
| Kilogram | kg | 1 | Body weight, commerce, SI base unit |
| Metric ton | t | 1,000 | Shipping, industrial materials |
| Ounce | oz | 0.0283 | Cooking, precious metals |
| Pound | lb | 0.4536 | Body weight, food, US commerce |
| Stone | st | 6.350 | Body weight (UK, Ireland) |
| Short ton | ton | 907.185 | US industrial and shipping |
Use Kilograms for Scientific Work: The kilogram is the SI base unit for mass. Use metric to avoid conversion errors in formulas.
Know Your Stone Conversion: In the UK and Ireland, body weight is expressed in stones and pounds (1 stone = 14 pounds).
- How was the kilogram redefined in 2019?
- It was redefined from a physical artifact to the fixed numerical value of the Planck constant, making it invariant across time and space.
- Why do some countries still use imperial units?
- The US uses customary units due to historical precedent and the high cost of conversion. The US Metric Conversion Act of 1975 made metric preferred but voluntary.
- How do I convert body weight for medical purposes?
- Weigh yourself in kilograms directly. For conversion, use 1 kg = 2.20462262185 lb (the exact definition from 1959).
- What is the difference between a metric ton and a short ton?
- A metric ton = 1,000 kg (2,204.6 lb). A short ton = 2,000 lb (907.2 kg). A long ton = 2,240 lb.
- How does cooking weight conversion differ?
- Recipes often use volume (cups, tablespoons), not weight. Different ingredients have different densities — 1 cup of flour = ~120 g, 1 cup of sugar = ~200 g.
- How do I convert between metric tons and shipping tons?
- In international shipping, freight is often calculated in cubic meters rather than weight, but when weight matters, metric tons (1,000 kg) are the standard. However, maritime shipping may use the freight ton (1 cubic meter or 1,000 kg, whichever is greater) for rate calculation. For air freight, chargeable weight is the greater of actual weight and volumetric weight (length x width x height / 6000 in cm), which means a lightweight large box can cost more than a small heavy one even though their masses differ significantly.
- Why does gold use different weight units?
- Precious metals including gold, silver, platinum, and palladium are traded in troy ounces (31.1035 g), not avoirdupois ounces (28.3495 g). A troy ounce is about 9.7% heavier than a standard ounce. Gold bar weights are typically expressed in kilograms or troy ounces — a standard Good Delivery gold bar weighs approximately 400 troy ounces (12.4 kg). When using this calculator, note that "ounce" refers to the avoirdupois ounce used for everyday measurements, not the troy ounce used for precious metals.
- Mass only, not weight-force: Does not convert to newtons or adjust for gravity.
- No troy or specialty units: Troy ounces, carats, grains not included.
- No apothecary units.
- Rounding precision: Results rounded to 4-6 significant digits.
- Based on 1959 International Yard and Pound Agreement (1 lb = 0.45359237 kg exactly).
Unusual Weight Units and Specialist Applications
While this calculator covers the most common mass units, many specialized fields use additional units that are not included. The troy ounce (31.1035 g) is the standard unit for precious metals like gold, silver, and platinum — it is different from the avoirdupois ounce (28.3495 g) used for everyday measurements. The carat (200 mg) is used exclusively for gemstones. The grain (64.8 mg) persists in ammunition and archery for measuring bullet and arrow weights. The slug (14.5939 kg) is the imperial unit for mass in the gravitational foot-pound-second system, used in engineering and physics contexts where the distinction between mass and weight matters.
Historical weight units add another layer of complexity for researchers, historians, and antique dealers. The stone varied by region and commodity historically — a stone of wool was different from a stone of meat. The hundredweight (cwt) also varied: a US short hundredweight is 100 lb, while a UK long hundredweight is 112 lb. The ton similarly has three variants: the short ton (2,000 lb), the long ton (2,240 lb), and the metric ton (1,000 kg). These historical variations are important when interpreting historical documents, evaluating antiques, or researching pre-20th century trade records.
- BIPM — Definition of the kilogram
- NIST — Official US source for measurement standards
- NIST Special Publication 811 — Guide for the Use of SI
- International Yard and Pound Agreement (1959)
Last updated: May 12, 2026