How to use the mass calculator
Type the number, choose the unit it's written in, and choose the unit you want. Quick buttons cover the common pairs: lb to kg, kg to lb, oz to g, g to oz, troy oz to g and tonne to US ton. Swap flips the direction.
Use the unit on the label, not the one you expect. A food package marked 16 oz means ordinary ounces. A gold coin marked 1 oz usually means a troy ounce, which is heavier.
- Enter the mass. Zero is allowed, and you can type scientific notation like 2.5e-6.
- Choose the source unit, checking whether an ounce is ordinary or troy and which kind of ton you have.
- Choose the target unit or tap a quick pair.
- Pick how many significant digits to show (4 to 12).
- Press Convert mass and read the result, the direct factor and the reverse check.
Kg to lbs and lbs to kg chart
Both directions use the exact definition of the pound, 0.45359237 kg. Values are rounded to two decimals.
| Kilograms | Pounds | Pounds | Kilograms |
|---|---|---|---|
| 1 kg | 2.20 lb | 1 lb | 0.4536 kg |
| 5 kg | 11.02 lb | 5 lb | 2.27 kg |
| 10 kg | 22.05 lb | 10 lb | 4.54 kg |
| 20 kg | 44.09 lb | 50 lb | 22.68 kg |
| 50 kg | 110.23 lb | 100 lb | 45.36 kg |
| 70 kg | 154.32 lb | 150 lb | 68.04 kg |
| 80 kg | 176.37 lb | 180 lb | 81.65 kg |
| 100 kg | 220.46 lb | 200 lb | 90.72 kg |
The conversion formula
Every unit has a fixed value in kilograms. The calculator multiplies your number by the source unit's value to get kilograms, then divides by the target unit's value. Running the answer back the other way must return your original number, which is the reverse check you see in the result.
For 150 lb: 150 x 0.45359237 = 68.0388555 kg. Back again: 68.0388555 / 0.45359237 = 150 lb.
Mass in kg = value x kg per source unitResult = mass in kg / kg per target unitDirect factor = source kg factor / target kg factorReverse check = result x target kg factor / source kg factor
Worked mass conversion examples
These examples show why the unit name matters as much as the number.
| Conversion | Math | Result | Why the label matters |
|---|---|---|---|
| 150 lb to kg | 150 x 0.45359237 | 68.0388555 kg | Pound means the ordinary pound |
| 1 kg to lb | 1 / 0.45359237 | 2.20462262 lb | The reverse of the pound definition |
| 1 troy oz to g | 1 x 31.1034768 | 31.1034768 g | An ordinary ounce is 28.349523125 g |
| 250 ct to g | 250 x 0.2 | 50 g | A metric carat is 0.2 g |
| 1 tonne to US ton | 1,000 / 907.18474 | 1.10231131 US tons | Metric and short tons differ |
Ounces, stones and tons: which one do you have?
An ordinary (avoirdupois) pound has 16 ounces, and each ounce is 28.349523125 g. Precious metals use troy ounces of 31.1034768 g, about 9.7% heavier, with 12 troy ounces to a troy pound. The calculator labels troy results oz t and lb t so they can't be mixed up.
A stone is 14 lb, or 6.35029318 kg, and the result shows a stones-and-pounds reading: 150 lb is 10 st 10 lb. Tons come in three sizes. A US short ton is 2,000 lb (907.18474 kg), a metric tonne is 1,000 kg, and a long ton is 2,240 lb (1,016.0469088 kg).
Is this a weight converter or a mass converter?
Both, in everyday terms. Scales and labels say weight but report kilograms or pounds, which are units of mass. In physics, weight is the force gravity puts on a mass, measured in newtons, and it changes if gravity changes. Your mass doesn't.
This calculator converts mass units only. It doesn't work out force in newtons or pounds-force, and it won't convert cups or liters to grams, because that needs the material's density. It also can't make a scale more accurate than it is, so round your answer to what the scale can read.
Sources
These references back up the definition of the kilogram and every conversion factor on this page.