How to use the Weight Converter
- Enter the mass you want to convert.
- Pick the unit it is currently in and the unit you want.
- Check which ton you mean before converting — short, long and metric all differ.
- For body weight in stones and pounds, convert the pounds portion separately and add it.
- Read the three alternate units underneath for a quick sanity check.
How the calculation works
All units convert through the kilogram, the SI base unit of mass, redefined in 2019 in terms of the Planck constant rather than a platinum-iridium cylinder in Sèvres. The avoirdupois pound has been defined as exactly 0.45359237 kg since 1959, which makes every pound-to-kilogram conversion exact and every ounce exactly 28.349523125 g.
Three different tons are in everyday circulation and they are not close enough to be interchangeable. The metric tonne is 1,000 kg, the US short ton is 2,000 lb (907.18 kg) and the UK long ton is 2,240 lb (1,016.05 kg). A shipment quoted as 100 tons could differ by nearly 11 tonnes depending on which is meant, which is precisely why freight documents specify the ton type explicitly.
Strictly speaking these are units of mass, not weight: weight is a force and varies with local gravity, while mass does not. The distinction only bites in physics and engineering contexts, where a 70 kg mass weighs about 686 newtons on Earth and roughly a sixth of that on the Moon. For commerce and body weight, the everyday usage is universally understood and harmless.
mass_target = (mass_source × kg_per_source) ÷ kg_per_target; 1 lb = 0.45359237 kg exactly; 1 oz = lb/16; 1 stone = 14 lbSource: International Yard and Pound Agreement (1959); BIPM SI Brochure 9th edition (2019 kilogram redefinition); NIST Handbook 44.
Worked example
A recipe scaled for a commercial kitchen calls for 12 lb 8 oz of dough and the mixer reads in kilograms.
- Convert to a single unit: 12 lb + 8/16 lb = 12.5 lb.
- Enter 12.5 and select pounds as the source.
- Select kilograms: 12.5 × 0.45359237 = 5.6699 kg.
- Round for the scale display: 5.67 kg.
12 lb 8 oz is 5.67 kg — and because the pound is exactly defined, the only rounding is the one you choose at the end.
Frequently asked questions
How many pounds are in a stone?+
Exactly 14. A weight of 11 st 4 lb is 158 lb, or 71.67 kg.
Which ton should I use?+
In the US, 'ton' normally means the 2,000 lb short ton. In metric contexts it means the 1,000 kg tonne. The UK long ton of 2,240 lb persists in some shipping documentation.
Is a fluid ounce the same as an ounce?+
No. A fluid ounce measures volume, an ounce measures mass. They coincide only for water, and even then only approximately.
Are troy ounces included?+
Not here — troy weight is used for precious metals and runs on a different scale, where one troy ounce is 31.1035 g against the avoirdupois 28.3495 g.
Last reviewed September 1, 2026. We review this page whenever the underlying formula, tax year, published rate or standard changes.