Weight Converter

Weight conversions move between the metric units (gram, kilogram) and the imperial ones (ounce, pound, stone). The gram is the base here.

Metric:

• 1 gram = 1,000 mg = 0.001 kg

Imperial:

• 1 ounce = 28.3495 g
• 1 pound = 453.592 g (16 ounces)
• 1 stone = 6,350.29 g (14 pounds)

Quick cross-system:

• 1 kg = 2.20462 lbs
• 1 lb = 0.453592 kg

For a sense of scale:

• A paperclip: about 1 g
• A smartphone: 170-200 g
• A liter of water: almost exactly 1 kg
• An average adult: about 70 kg (154 lbs, or 11 stone)

The stone still rules personal body weight in Britain and Ireland, where people say “eleven stone” the way Americans say “154 pounds.” It throws off travelers because it shows up almost nowhere else.

The real trap is the ounce, because there are two completely different ones. The weight ounce (28.35 g) measures mass; the fluid ounce measures volume. A recipe calling for “8 oz of flour” (weight) and “8 fl oz of milk” (volume) wants two unrelated quantities that happen to share a name. They only line up for water, where one fluid ounce weighs almost exactly one ounce, which is the historical coincidence that started the whole muddle.

The third ounce nobody warns you about

There is also the troy ounce, at 31.1035 g, and it is about 10 percent heavier than the ordinary avoirdupois ounce. Precious metals are the one place it survives. A one-ounce gold coin contains a troy ounce, so it weighs 31.1 g, not 28.35, and gold prices quoted “per ounce” always mean troy. Mixing the two up costs 10 percent, which on a metal priced in the thousands is not a rounding error.

The troy pound is worse, because it holds 12 troy ounces rather than 16, making it lighter than the ordinary pound at 373.24 g. It is essentially extinct outside bullion assay, but it is why the old riddle about a pound of feathers and a pound of gold has an answer: the feathers are heavier.

Mass versus weight

Strictly, everything on this page converts mass. Weight is a force, and it changes with gravity while mass does not. A 70 kg person still has 70 kg of mass on the Moon but weighs about a sixth as much, which is why a bathroom scale there would read roughly 11.6 kg.

For every practical purpose on Earth the distinction does not matter, because scales are calibrated for local gravity. It matters in physics problems, and it is why the SI unit of force is the newton rather than the kilogram. One kilogram of mass weighs about 9.81 newtons at sea level.

Gravity does vary slightly across the Earth’s surface, by about 0.5 percent between the poles and the equator. A precision balance that has been moved between continents genuinely needs recalibrating, which is a real nuisance in laboratories and a complete non-issue in kitchens.