Weight/mass unit reference table
Exact grams-equivalents for every unit supported by this converter, per NIST Special Publication 811.
| Unit | Symbol | Grams equivalent |
|---|---|---|
| Milligram | mg | 0.001 g |
| Gram | g | 1 g |
| Kilogram | kg | 1,000 g |
| Metric tonne | t | 1,000,000 g |
| Ounce (avoirdupois) | oz | 28.349523125 g |
| Pound (avoirdupois) | lb | 453.59237 g |
| Stone | st | 6,350.29318 g |
- This converter uses avoirdupois ounces and pounds (the everyday, commercial system), not troy ounces/pounds, which are used for precious metals and have different values.
- "Tonne" here means the metric tonne (1,000 kg); it is not the same as the US short ton (2,000 lb ≈ 907.18 kg) or the UK long ton (2,240 lb ≈ 1,016.05 kg).
- The kilogram's definition changed in 2019 from a physical reference artifact to a fixed value of the Planck constant, with no practical effect on everyday conversions.
How are weight and mass units defined?
The kilogram is the SI base unit of mass, and since the 2019 revision of the International System of Units it is defined by fixing the Planck constant at an exact numerical value, replacing the former physical prototype kilogram. The avoirdupois pound — the everyday pound used in the US and UK for body weight and general goods — was fixed as exactly 453.59237 grams by the same 1959 international yard-and-pound agreement that defined the yard. The ounce (1⁄16 pound = 28.349523125 g) and the stone (14 pounds = 6,350.29318 g, a UK/Ireland customary unit still common for body weight) follow directly from that exact pound figure. This converter's "tonne" option is the metric tonne (1,000 kg), distinct from the US short ton (2,000 lb) and UK long ton (2,240 lb).
Strictly, physicists distinguish mass (the invariant amount of matter in an object, measured in kilograms) from weight (the force gravity exerts on that mass, measured in newtons and dependent on location). In everyday commerce, cooking and this converter, however, "weight" is used in its common, non-technical sense to mean mass — the same convention NIST documents note is standard in trade and industry, even though it is not strictly correct in physics.
How to use this weight converter
- Enter the weight (mass) value you want to convert.
- Select the unit that value is currently in, from milligrams up to stone or metric tonnes.
- Read the converted results in kilograms, grams, ounces, pounds and stone, shown at once.
- For body-weight figures given in stone and pounds together (a common UK format, e.g. "11 st 6 lb"), convert the stone and pound parts separately and add the results.
The formula behind weight conversion
Every input value is first converted to grams using its exact metric or avoirdupois factor, then re-expressed in each other unit by dividing by that unit's own grams-equivalent. All the imperial figures below are exact defined values, not measured approximations.
Common mistakes
- Treating weight and mass as always interchangeable — physically, weight is a force that varies with local gravity, while mass (what this converter, like commercial "weight" tools, actually converts) is invariant.
- Confusing avoirdupois ounces/pounds (used here, and for everyday goods and body weight) with troy ounces (used for precious metals, where 1 troy oz = 31.1034768 g, about 10% heavier than an avoirdupois ounce).
- Confusing the metric tonne (1,000 kg) with the US short ton (2,000 lb) or UK long ton (2,240 lb) — this converter's tonne option is the metric tonne only.
- Rounding to whole grams or kilograms too early in a multi-step conversion, which compounds small errors across several unit changes.
Domande frequenti
How many grams are in a pound?
One avoirdupois pound equals exactly 453.59237 grams, a value fixed by the 1959 international yard-and-pound agreement — the same agreement that defined the yard in metric terms. This is the everyday pound used for body weight and general goods in the US and UK.
How many pounds are in a stone?
One stone equals exactly 14 pounds, or 6,350.29318 grams. The stone is a customary unit still commonly used for body weight in the UK and Ireland, though it has no formal role in the SI or in most other countries.
Is weight the same as mass?
Not physically — mass is the invariant amount of matter in an object (measured in kilograms), while weight is the gravitational force acting on that mass (measured in newtons, and slightly dependent on location). In everyday commerce, cooking and converters like this one, "weight" is used informally to mean mass, which is the standard convention this tool follows.
Is an ounce always the same size?
No. This converter uses the avoirdupois ounce (28.349523125 g), the standard for everyday goods and body weight. The troy ounce, used for precious metals such as gold and silver, is a different unit equal to 31.1034768 g — about 10% heavier — and is not one of the units this converter supports.
Is a metric tonne the same as a US ton?
No. A metric tonne is exactly 1,000 kilograms (about 2,204.6 lb). The US short ton is 2,000 pounds (about 907.18 kg) and the UK long ton is 2,240 pounds (about 1,016.05 kg) — both lighter and heavier respectively than the metric tonne. This converter's "tonne" option refers to the metric tonne only.
Fonti
- National Institute of Standards and Technology (NIST). Special Publication 811: Guide for the Use of the International System of Units (SI), 2008 Edition (includes guidance distinguishing mass and weight in common usage).
- Astin AV, Karo HA. Refinement of Values for the Yard and the Pound. National Bureau of Standards, 1959 (the international yard-and-pound agreement fixing the avoirdupois pound).
- International Bureau of Weights and Measures (BIPM). The International System of Units (SI Brochure), 9th edition, 2019 — 2019 redefinition of the kilogram via the Planck constant.
- NIST Handbook 44, Appendix C: General Tables of Units of Measurement.