Weight & Mass Conversions
Everything here ties back to the kilogram. Below: how the math works, what each unit is for, and the weight-vs-mass distinction that matters in physics but not on your bathroom scale.
How the converter works
Every unit is defined in terms of the kilogram (the SI base unit of mass). We convert your value to kilograms, then to the unit you chose.
Result = Value × (source unit in kg) ÷ (target unit in kg)
Example: 5 pounds to grams → 5 × 0.453592 ÷ 0.001 = 2,267.96 g. The kg cancels out and you get a direct ratio.
Units and what they're for
Kilogram (kg)
1 kg = base unit
Since 2019 the kilogram has been defined by fixing the Planck constant; before that it was a physical platinum-iridium cylinder in Sèvres, France — the last SI unit tied to an artifact.
Gram (g)
1 g = 0.001 kg
Originally the mass of 1 cm³ of water at 4°C. You see grams on nutrition labels, recipes, and postage. Most of the world sells food by grams.
Milligram (mg)
1 mg = 0.000001 kg
A thousandth of a gram. Drug doses are in mg; so are sodium and vitamins on labels. Water quality often uses mg/L (same as parts per million).
Pound (lb)
1 lb ≈ 0.453592 kg
The everyday pound in the US and UK is the avoirdupois pound (16 oz). "Lb" comes from libra pondo. US law sets 1 lb = 0.45359237 kg exactly.
Ounce (oz)
1 oz ≈ 0.0283495 kg
One sixteenth of an avoirdupois pound. US food and postage use this. Precious metals use the troy ounce (31.1035 g); we use the standard ounce.
Metric ton (t)
1 t = 1,000 kg
Often called a "tonne" to avoid mixing with the US short ton (2,000 lbs) or UK long ton (2,240 lbs). Shipping, agriculture, and emissions use the metric ton. 1 t ≈ 2,204.62 lbs.
Quick reference
Formulas and examples for the conversions people use most.
| From | To | Formula | Example |
|---|---|---|---|
| Kilograms | Pounds | kg × 2.20462 | 70 kg = 154.32 lbs |
| Pounds | Kilograms | lbs × 0.453592 | 150 lbs = 68.04 kg |
| Pounds | Ounces | lbs × 16 | 5 lbs = 80 oz |
| Ounces | Pounds | oz ÷ 16 | 32 oz = 2 lbs |
| Ounces | Grams | oz × 28.3495 | 8 oz = 226.80 g |
| Grams | Ounces | g × 0.035274 | 500 g = 17.64 oz |
| Metric Tons | Pounds | t × 2,204.62 | 2 t = 4,409.24 lbs |
| Milligrams | Grams | mg ÷ 1,000 | 500 mg = 0.5 g |
Weight vs. mass
We use the words interchangeably, but they're not the same.
Mass
The amount of matter in an object. It doesn't change with location — a 70 kg person has 70 kg of mass on Earth, on the Moon, or in space. SI unit: kilogram. You measure it with a balance (comparison to known masses).
Weight
The force of gravity on that mass. It does change with location: same 70 kg person is about 686 N on Earth and ~114 N on the Moon. SI unit: newton. A spring scale measures weight; it depends on local g (9.81 m/s² on Earth).
On Earth, g is almost constant, so the difference rarely matters. Bathroom scales say "kg" or "lbs" — they're measuring weight but showing you the equivalent mass.
Where the units came from
The gram was first defined in 1795 as the mass of 1 cm³ of water at 4°C — tying mass to volume. The kilogram took over as the base unit because a gram was too small for daily use.
Imperial units came from old trading standards. The avoirdupois pound was finally pinned down in 1959: English-speaking countries agreed on exactly 0.45359237 kg, which ended years of tiny differences between them.
"Ton" is a mess: US short ton (2,000 lbs), UK long ton (2,240 lbs), and metric ton (1,000 kg) are all different. International trade and science usually use the metric ton (tonne) so everyone means the same thing.
Weight conversion FAQ
How many pounds are in a kilogram?
About 2.20462. So 70 kg ≈ 154.32 lbs. Multiply kg by 2.20462 to get pounds.
What's the difference between weight and mass?
Mass is how much stuff is in an object (kg or g); weight is the pull of gravity on it (newtons). On Earth we usually say "weight" when we mean mass because gravity is almost the same everywhere here.
How many grams are in an ounce?
One avoirdupois ounce (the one used for food and postage) is about 28.3495 g. Precious metals use the troy ounce, which is 31.1035 g. This converter uses the standard ounce.
How many ounces are in a pound?
There are exactly 16 ounces in 1 pound. Quick checks: 2 pounds = 32 ounces, 5 pounds = 80 ounces, and 10 pounds = 160 ounces.
How many pounds are in an ounce?
One ounce is 0.0625 pounds (1/16 of a pound). To convert ounces to pounds, divide by 16. Example: 40 oz ÷ 16 = 2.5 lbs.
How many grams are in a pound?
One pound is exactly 453.59237 grams. For quick math, many people round to 454 g per pound. Example: 3 lbs ≈ 1,360.78 g.
How do you convert metric tons to pounds?
1 metric ton (tonne) = 1,000 kg ≈ 2,204.62 lbs. Multiply tonnes by 2,204.62. For comparison: US short ton is 2,000 lbs, UK long ton is 2,240 lbs.