Gera Tools

Mass Unit Conversion Reference

Convert kg, lb, oz, stone, tonne, and troy ounce.

Reference table and live converter for mass units across SI, avoirdupois, troy, and ton scales. Enter a value in any unit and see kilograms, grams, pounds, ounces, stone, tonnes, troy ounces, and carats using exact factors. It runs free in your browser on Gera Tools, with nothing uploaded.

Last updated Source: Gera Tools

How many kilograms are in a pound?

Exactly 0.45359237 kg. The avoirdupois pound has this exact international definition, so an avoirdupois ounce (one-sixteenth of a pound) is 0.028349523125 kg.

Mass units split into several incompatible families — metric SI, everyday avoirdupois, the troy system for precious metals, and various tons — which makes a reliable converter genuinely useful. Enter a value in any unit and this reference shows it in every other, using exact factors.

The mass unit families

These families evolved separately and are not interchangeable without a converter:

SI / metric — the kilogram (kg) is the base unit; grams, milligrams, and tonnes (1,000 kg) are the common scale points. Used in science, medicine, and most of the world.

Avoirdupois — the everyday system in the UK and US for general goods. The pound (lb) is the central unit (16 oz = 1 lb, 14 lb = 1 stone). The avoirdupois ounce (28.3495 g) is what you see on food labels and kitchen scales.

Troy — used exclusively for precious metals and gemstones. The troy ounce (31.1035 g) is about 10% heavier than the avoirdupois ounce. Spot prices for gold, silver, platinum, and palladium are always quoted per troy ounce; using the wrong ounce in a metals trade is a serious error.

Tons — three different “tons” exist. The metric tonne is 1,000 kg. The US short ton is 2,000 lb (approximately 907 kg). The UK long ton is 2,240 lb (approximately 1,016 kg). Commodity markets, shipping, and industrial sectors may use any of the three.

How it works

Each unit stores an exact number of kilograms per unit, so the kilogram is the shared base. Conversion is two steps:

kilograms = value × kgPerUnit[from]
result    = kilograms ÷ kgPerUnit[to]

The avoirdupois pound is exactly 0.45359237 kg, and the ounce is one-sixteenth of that. The troy system is separate: a troy ounce is 0.0311034768 kg, heavier than an avoirdupois ounce, which is why precious-metal quotes use it. The three “tons” are distinct: metric tonne 1000 kg, US short ton 907.18474 kg, and UK long ton 1016.0469088 kg.

Worked examples

  • Body weight: To convert 70 kg to stone and pounds: 70 ÷ 6.35029 ≈ 11 stone, remainder 70 − (11 × 6.35029) ≈ 1.15 kg ≈ 2.5 lb, so approximately 11 st 2.5 lb.
  • Precious metals: A gold bar described as “400 troy ounces” (the London Good Delivery bar standard) weighs 400 × 31.1035 ≈ 12,441 g ≈ 12.44 kg.
  • Gemstone: A 2-carat diamond weighs exactly 2 × 0.2 g = 0.4 g. The metric carat (exactly 0.2 g) is defined under SI and is not a mass for everyday goods.
  • Shipping: A freight invoice quoting 5 US short tons is 5 × 907.185 = 4,535.9 kg, or 4.536 metric tonnes.

Tips and notes

  • For gold and silver, always use the troy ounce (≈ 31.10 g), not the kitchen ounce (≈ 28.35 g) — the ~10% difference matters significantly in any metals transaction.
  • UK body weight is still often quoted in stone and pounds; metric equivalents are approximate but useful for medical and scientific contexts.
  • When a contract or commodity quote says “ton” without qualification, confirm which ton applies before converting — the metric, short, and long ton differ by up to about 12%.

Very large or very small results display in scientific notation. All conversions run locally in your browser.