About the Weight Converter

The weight converter translates between metric and imperial units of mass, including milligrams, grams, kilograms, tonnes, ounces, pounds, stones, and US tons. Whether you are reading a European recipe in grams, an American supplement label in ounces, or a British body-weight measurement in stones, this tool gives you an instant conversion in either direction.

Strictly speaking, this converter handles mass rather than weight. Mass is the amount of matter in an object and is measured in grams; weight is the gravitational force on that mass and is measured in newtons. In everyday usage the two are conflated, and pounds, ounces, and stones are used as units of mass. For precise physics work, the distinction matters; for cooking, shopping, and body weight, the converter's output is what you need.

The metric system uses the gram as its base unit, with prefixes for thousandths (milligrams), thousands (kilograms), and millions (tonnes). The imperial system uses the ounce, pound (16 ounces), and stone (14 pounds), with the US ton (2000 pounds) for very large masses.

How It Works

Each unit has a defined relationship to the gram, the base unit of mass in the CGS system. The converter uses these factors to translate between any two units:

1 mg   = 0.001 g
1 g    = 1 g
1 kg   = 1000 g
1 t    = 1,000,000 g      (metric tonne)
1 oz   = 28.349523125 g   (exact, avoirdupois)
1 lb   = 453.59237 g      (exact, 16 ounces)
1 st   = 6350.29318 g     (14 pounds)
1 ton  = 907184.74 g      (US short ton, 2000 pounds)

The conversion proceeds in two steps: the input is multiplied by the source unit's factor to give a mass in grams, then divided by the target unit's factor to give the result in the target unit. This two-step approach through a common base unit is exact and easy to verify.

The avoirdupois ounce and pound were standardised internationally in 1959, with the pound defined as exactly 453.59237 grams. This differs from the troy ounce (about 31.1 grams) used for precious metals, which this converter does not handle. The metric tonne (1000 kilograms) differs from the US short ton (2000 pounds, about 907 kilograms) and the British long ton (2240 pounds, about 1016 kilograms).

Worked Examples

To convert 1 kilogram to pounds, the calculation is 1000 / 453.59237 = 2.20462 pounds. This is the conversion factor used on food labels and in fitness tracking apps.

To convert 150 pounds to kilograms, the calculation is 150 * 453.59237 / 1000 = 68.039 kilograms. This is a typical adult body weight converted between the two systems.

To convert 1 stone to pounds, the calculation is 6350.29318 / 453.59237 = 14 pounds exactly, since one stone is defined as 14 pounds. To convert 11 stone to kilograms, the calculation is 11 * 6350.29318 / 1000 = 69.85 kilograms, a typical body weight in the British system.

When to Use This Tool

Use the weight converter whenever you need to translate between metric and imperial mass units:

Reading international recipes that use grams instead of ounces.
Converting body weight between kilograms, pounds, and stones.
Interpreting supplement or medication labels from another country.
Calculating postage for packages measured in different units.
Comparing the weight of products sold in different markets.
Working with bulk materials measured in tonnes or tons.
Teaching the relationships between metric and imperial mass units.

Limitations & Disclaimer

This converter handles avoirdupois units only and does not convert troy ounces (used for precious metals), carats (used for gemstones), or pharmaceutical units. The distinction between mass and weight is not enforced; for physics work requiring force units, use newtons. Very large or very small results may be displayed in scientific notation. See our disclaimer for full details.

Frequently Asked Questions

What is the difference between mass and weight?

Mass is the amount of matter in an object and is measured in grams or kilograms. Weight is the gravitational force on that mass and is measured in newtons. In everyday usage the two are conflated, and pounds, ounces, and stones are treated as units of mass. For precise physics work, the distinction matters because weight depends on gravity.

What is the difference between a tonne and a ton?

A tonne (metric ton) is 1000 kilograms, about 2204.6 pounds. A US short ton is 2000 pounds, about 907.2 kilograms. A British long ton is 2240 pounds, about 1016 kilograms. The three differ by about 10%, so it is important to know which one a document refers to.

Why is the pound defined as exactly 453.59237 grams?

By international agreement in 1959, the avoirdupois pound was standardised as exactly 453.59237 grams to unify the American and British definitions, which previously differed by a tiny amount. This exact definition makes every conversion involving pounds reproducible to full floating-point precision.

What is a stone and where is it used?

A stone is 14 pounds, about 6.35 kilograms. It is used in the United Kingdom and Ireland primarily for body weight. A person who weighs 11 stone weighs 154 pounds or about 69.9 kilograms. The stone is rarely used outside the British Isles.

Does this converter handle troy ounces for precious metals?

No. The troy ounce (about 31.1 grams) is a different unit from the avoirdupois ounce (about 28.35 grams) used for everyday measurements. Precious metals, gemstones, and some pharmaceuticals use troy weight, which has its own system. This converter handles only avoirdupois units.

How accurate are the conversions?

The metric-to-metric conversions are exact. The imperial-to-metric conversions are exact by the 1959 international agreement. The only source of error is floating-point rounding, which is negligible for any practical purpose. The converter displays up to eight decimal places for precision.

Last updated: July 21, 2026 · Author: HT99 Tools Editorial Team · Reviewed by: HT99 Tools Editorial Team