Weight Converter

How do you convert weight units?

Any weight conversion works the same way: express the value in kilograms, then divide by the size of the unit you want. Each unit on this page has a fixed value in kilograms, so the method never changes, whether you are going from grams to ounces or from stone to pounds.

The two-step method

1. Multiply the value by the size of the starting unit in kilograms.
2. Divide that result by the size of the target unit in kilograms.

For example, to convert 12 ounces to grams: 12 × 0.028349523125 = 0.3401942775 kg, and 0.3401942775 ÷ 0.001 = 340.19 g. Most everyday pairs collapse into one factor. Multiply kilograms by 2.20462 to get pounds with the kg to lbs converter, multiply pounds by exactly 0.45359237 to get kilograms, or multiply ounces by 28.3495 to get grams. Going the other way, divide grams by 28.3495 to get ounces with the grams to ounces converter.

Mass versus weight

Strictly, kilograms, pounds and ounces measure mass, the amount of matter in an object. Weight in physics is the force gravity exerts on that mass, measured in newtons. A 10 kg bag has the same mass on the Moon, but it weighs about one sixth as much there. In everyday use, and on every bathroom and kitchen scale, “weight” means mass, which is how this converter treats it. If you need the force itself, use the force converter.

What is the SI unit of mass, and how is the kilogram defined?

The kilogram (kg) is the SI base unit of mass, defined since May 20, 2019 by fixing the Planck constant at exactly 6.62607015 × 10⁻³⁴ joule-seconds. The BIPM SI Brochure (9th edition) sets out this definition, which lets national laboratories realize the kilogram with a Kibble balance or by counting atoms in a silicon sphere. From 1889 until 2019 the kilogram was instead the mass of one physical object, the International Prototype of the Kilogram, a platinum-iridium cylinder kept at the BIPM near Paris.

How the pound and ounce hang off the kilogram

The 1959 International Yard and Pound Agreement fixed the avoirdupois pound at exactly 0.45359237 kg, and every customary mass unit follows from it. The grain is exactly 1/7,000 of a pound, or 64.79891 mg. The avoirdupois ounce is 437.5 grains (28.349523125 g), and the troy ounce is 480 grains (31.1034768 g), which is why a troy ounce is heavier than an ordinary one. The stone is 14 pounds (6.35029318 kg) and the US short ton is 2,000 pounds (907.18474 kg). NIST Handbook 44 lists these values for US trade.

Because mass is independent of gravity, a kilogram is a kilogram on any planet. Scales that weigh by force are calibrated to local gravity to show mass; to work with the force itself, use the force converter.

What are troy ounces, carats and stone?

A troy ounce (31.1034768 g) weighs precious metals, a metric carat (200 mg) weighs gemstones, and a stone (14 lb) measures body weight in the UK and Ireland. These specialist units share names with everyday ones but have different sizes, which is a common source of mistakes.

Troy ounce vs avoirdupois ounce

The ounce on food packaging and postal scales is the avoirdupois ounce, exactly 28.349523125 g, and 16 of them make a pound. Gold, silver and platinum are priced per troy ounce, exactly 31.1034768 g, which is about 9.7% heavier. A troy pound has only 12 troy ounces (373.24 g), so it is lighter than an ordinary 453.59 g pound. When you see a bullion price per ounce, it is always the troy ounce.

Metric carat

Gemstones are weighed in metric carats of exactly 200 mg, so 5 carats make 1 gram. The carat of mass is unrelated to the karat that describes gold purity. The carats to grams converter covers stone weights.

The stone

The stone equals 14 pounds (6.35029318 kg). It survives mainly in the UK and Ireland, where people still state body weight as, say, “11 stone 4”. There is no metric equivalent, so converting means going through pounds or kilograms.

Short, long and metric tons

A US (short) ton is 2,000 lb, or 907.18474 kg. A metric ton, or tonne, is 1,000 kg, about 2,204.62 lb. The British long ton of 2,240 lb (1,016.05 kg) is now rare. All three are simply called a “ton” in speech, so check which one a source means.

How much does a liter of water weigh?

One liter of water weighs very nearly 1 kilogram, or about 2.205 pounds, because the liter and the kilogram were originally linked through water. The match is close rather than exact: water is densest at about 4 °C and slightly lighter per liter when warm, so treat the figures below as good approximations.

The imperial gallon row is no coincidence: the British gallon was originally defined in 1824 as the volume of 10 pounds of water. For other liquids and for dry ingredients, volume and mass part ways, because a cup of flour weighs far less than a cup of water. The cups to grams converter uses ingredient densities for that, and the volume converter and liters to gallons converter handle the volume side.

Where is each weight unit used?

Grams and kilograms are the legal and everyday units almost everywhere, while the United States weighs people, food and parcels in pounds and ounces, and the UK still quotes body weight in stone. Science, medicine, trade and jewelry each add their own favorites.

• Grams and kilograms: food labels, recipes, body weight, parcels and trade in nearly every country; the kilogram is the legal base unit worldwide.
• Milligrams and micrograms: medicine doses, vitamins and nutrition labels, where tiny amounts matter.
• Pounds and ounces: body weight, groceries and shipping in the US; UK shops still show pounds alongside kilograms.
• Stone: body weight in the UK and Ireland, often combined with pounds.
• Metric tons: freight, mining, agriculture and emissions reporting internationally.
• US tons: vehicle load ratings, construction materials and scrap in the United States.
• Carats and troy ounces: jewelry, gemstones and precious-metal markets.

Cooking often mixes weight and volume. To turn grams of flour or sugar into cups you need the ingredient's density, which the cooking converter handles.