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Weight converter

Convert weight and mass units instantly — grams, kilograms, ounces, pounds, stone and tonnes, all at once with exact factors.

Sources: NIST — Guide to the SI, Appendix B.9 (conversion factors by kind of quantity: mass)

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Popular conversions

Milligrams (mg)
Grams (g)
Decagrams (dag)
Kilograms (kg)
Tonnes (t)
Ounces (oz)
Pounds (lb)
Stone (st)

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What the weight converter does

The weight converter turns a value in one mass unit into all the others at once — milligrams, grams, decagrams, kilograms, tonnes, ounces, pounds and stone. Type a number, pick the unit you’re converting from and the unit you want as your headline result, and every other unit updates below it immediately. No separate tool for “kg to lbs” and another for “g to oz” — one converter, eight units, always linked.

It earns its keep in the moments a unit mismatch actually matters: a bathroom scale in kilograms when the number on a US website is in pounds, a recipe written in ounces when your kitchen scale only does grams, a parcel limit given in kilograms when the airline prints it in pounds. The calculator uses exact definitional conversion factors, not rounded approximations, so the numbers hold up even at high precision — dosing, shipping weights, anything where “close enough” causes a real problem.

How to use the weight converter

  1. Enter a value. Any number, zero or greater, in any of the eight supported units.
  2. Pick the “From” unit. The unit your value is currently in.
  3. Pick the “To” unit. The unit you want as the headline result — the calculator still shows every unit at once, but this one is highlighted.
  4. Read the result. The converted value appears instantly, next to the same input expressed in all seven other units, so you can compare without retyping anything.

There’s no “convert” button and no page reload — the result updates as you type.

How the conversion works

Every unit converts through the kilogram, the calculator’s canonical unit. To go from unit A to unit B, the calculator multiplies the input by A’s kilogram-factor, then divides by B’s kilogram-factor — one multiplication, one division, nothing rounds in between.

The kilogram-factors themselves come from exact legal definitions, not from measurement:

  • 1 pound = 0.45359237 kilograms, exactly. This is set by the International Yard and Pound Agreement of 1959 (codified in NIST SP 811, Appendix B.9), which fixed the pound as an exact fraction of the kilogram for the US, UK and four other countries.
  • 1 ounce = 1/16 pound = 0.028349523125 kg, and 1 stone = 14 pounds = 6.35029318 kg — both exact, since each is defined as a fixed multiple of the pound (the stone by the UK’s Weights and Measures Act 1985).
  • 1 tonne = 1,000 kilograms, exactly — the metric ton, distinct from the US short ton or UK long ton.
  • Metric units (mg, g, dag, kg, t) are exact decimal multiples of the kilogram by definition, per the BIPM SI Brochure — that’s the whole point of the metric system. A decagram (dag) is 10 grams; you’ll mostly meet it in Central European recipes and shop labels.

Worked example

Convert 70 kg — an adult body weight — to pounds and stone:

  1. 70 kg is already in the canonical unit, so no first step is needed.
  2. 70 ÷ 0.45359237 (the kilogram-to-pound factor) = 154.324 lb.
  3. 70 ÷ 6.35029318 (the kilogram-to-stone factor) = 11.0231 st.

That same 70 kg also equals 70,000 g and 0.07 t — the weight converter shows all of them from that single input, without any extra steps.

Metric vs. imperial — and the myths people repeat

Metric units scale by powers of ten — 1 kg = 1,000 g = 100 dag — so moving between them is just shifting a decimal point. Pounds, ounces and stone scale by the traditional factors above (16, 14), inherited from historical trade measures and frozen in place by the 1959 agreement. That mismatch is why two popular shortcuts fall apart under scrutiny: a pound is not “about 500 grams” (it’s 453.59 g, an 11% difference that adds up fast when you scale a recipe), and a kilogram is not “2 pounds” (it’s 2.20462 lb — round it down and a 100 kg weight limit becomes a 220 lb one instead of 220.5 lb).

Where weight conversion comes up

Body weight is the most common one — scales, medical charts and fitness apps split between kilograms, pounds and stone depending on the country (the UK and Ireland still weigh people in stone and pounds). Cooking and baking mix grams and ounces constantly, since US recipes lean on ounces and pounds while most of the world measures in grams. Medication and supplement dosing is usually given in milligrams, with the occasional gram-scale conversion for larger doses. Shipping, freight and vehicle weights are quoted in tonnes or kilograms depending on the carrier and country. And the decagram — 10 grams — still shows up on Central European grocery scales and in older recipes, even though it’s rare almost everywhere else.

Frequently asked questions

How many pounds are in a kilogram?

1 kilogram equals 2.20462 pounds, following from the exact definition 1 lb = 0.45359237 kg. It’s not a round number, so a “2 lb per kg” shortcut drifts further from the truth the larger the value gets — at 100 kg the error is already almost 5 lb.

How many kilograms are in a pound?

1 pound equals exactly 0.45359237 kilograms. This isn’t a rounded measurement — it’s the legal definition fixed by the International Yard and Pound Agreement of 1959, used identically in the US, UK, Canada, Australia and other countries.

How many grams are in an ounce?

1 ounce equals exactly 28.349523125 grams, because an ounce is defined as 1/16 of a pound and the pound itself is fixed at 0.45359237 kg. For everyday cooking, rounding to 28.35 g is more than precise enough.

Is a pound the same as 500 grams?

No. A pound is 453.59 grams, not 500 g — a difference of about 46.4 g, or roughly 10%. The “pound equals 500 g” shortcut is common but wrong; it likely comes from confusing the imperial pound with a metric “pound” (½ kg) used informally in some European countries.

How much is a stone in kg?

1 stone equals exactly 6.35029318 kilograms. A stone is defined as 14 pounds, and since a pound is fixed at 0.45359237 kg, the stone-to-kilogram figure follows directly and exactly from that.

How many pounds are in a stone?

1 stone equals exactly 14 pounds, by definition (UK Weights and Measures Act 1985). Stone is used almost exclusively for body weight in the UK and Ireland — “11 stone” means 154 pounds, or about 69.9 kg.

How many kilograms are in a metric ton?

1 metric tonne equals exactly 1,000 kilograms. It’s distinct from the US short ton (about 907.18 kg) and the UK long ton (about 1,016.05 kg) — when a source just says “ton” without specifying, check which one it means before converting.

Is 1 kg equal to 2 pounds?

Not quite — 1 kg is 2.20462 pounds, about 10% more than 2 lb. The “kg equals 2 lb” shortcut is close enough for a rough mental estimate, but it understates the true weight, and the gap grows with larger values.

How many ounces are in a pound?

1 pound equals exactly 16 ounces, by definition — this is one of the few imperial relationships that’s a clean whole number, unlike the pound-to-kilogram conversion.

What is 100g in ounces?

100 grams equals about 3.53 ounces (3.5274 oz precisely). This comes up constantly in recipes written in ounces when you’re weighing ingredients on a metric kitchen scale.

Sources