Weight Converter

This converter changes a mass value between the seventeen units the tool supports — grams, kilograms, milligrams and micrograms; pounds and ounces in both avoirdupois and troy; long, short, metric and assay tons; hundredweight in both forms; metric carats; and the atomic mass unit. Enter the figure, choose the two units, read the answer.

The reason there are so many is that several trades never adopted the metric system and several others use a system of their own. Precious metals, gemstones, shipping and chemistry each measure mass differently, and the same word can mean different amounts in each.

Which conversions come up most?

The everyday ones, all of which are exact by definition:

• 1 pound = 453.59237 g exactly
• 1 ounce = 28.349523125 g (one sixteenth of a pound)
• 1 kilogram = 2.204623 lb
• 1 metric carat = 200 mg exactly

The pound was fixed at exactly 0.45359237 kilograms by international agreement in 1959, which is why these are exact figures rather than measurements that get refined over time.

A worked example: a parcel

A courier quotes by the kilogram and your scales read 2.5 lb.

• 2.5 × 0.45359237 = 1.134 kg

Just over a kilo, which on most tariffs means paying for two. Worth knowing before you add packaging.

The ton problem

"Ton" is the single most dangerous word in this list, because it names three different masses:

• Metric ton (tonne) — 1,000 kg
• Long ton (UK, imperial) — 1,016.047 kg, or 2,240 lb
• Short ton (US) — 907.185 kg, or 2,000 lb

The spread between the smallest and the largest is about 12%. On a single shipping container that is more than a tonne of difference, so a contract or freight document that says only "tons" is worth querying rather than converting.

The assay ton in the list is something else again — 29.167 grams, a laboratory quantity used in ore assaying, sized so that the milligrams of metal recovered from it give the troy ounces per ton directly.

Troy and avoirdupois

Gold, silver and platinum are weighed in troy ounces; everything else in the English-speaking world uses avoirdupois. They are not the same:

• 1 avoirdupois ounce = 28.3495 g
• 1 troy ounce = 31.1035 g

A troy ounce is about 10% heavier. To make it worse, a troy pound is twelve troy ounces rather than sixteen, so a troy pound is lighter than an ordinary pound even though the ounce is heavier. If you are pricing bullion, check which ounce the quote uses — the difference is roughly the same size as a decent price movement.

How to use the converter

1. Type the mass you have into the box.
2. Select its unit, paying attention to troy versus ordinary and which ton.
3. Select the unit you want.
4. Read the result and copy it.

Where the awkward units actually appear

Recipes are the most common source of trouble, because American recipes measure dry ingredients by volume and European ones by mass, and converting between them needs the density of the specific ingredient rather than a unit factor. Shipping is the next, where the three tons collide with volumetric weight rules. Jewellery and bullion bring in troy ounces and carats together, often on the same invoice. Laboratory work uses micrograms and atomic mass units at one end and assay tons at the other. The converter covers all of them, but it can only convert mass to mass — anything involving density needs the substance as well as the number.

Frequently asked questions

How many grams are in a pound?

453.59237 exactly. For kitchen work, 454 g is close enough; for anything metered or sold by weight, use the full figure.

What is the difference between mass and weight?

Mass is how much matter something contains and does not change with location; weight is the force gravity exerts on that mass. Every unit here is strictly a mass unit, even the ones named "weight" in everyday speech. It only matters in physics problems and off the Earth.

Why is a carat 200 milligrams?

The metric carat was standardised at exactly 0.2 grams in the early twentieth century to replace a set of local carats that varied between markets. Do not confuse it with the karat that describes gold purity, which is not a mass at all.

What is a hundredweight?

112 pounds in the long (British) form, 100 pounds in the short (American) form. Twenty hundredweight make a ton in each system, which is why the two tons differ.

What is the atomic mass unit for?

Chemistry and physics. One unified atomic mass unit is one twelfth of the mass of a carbon-12 atom, about 1.66 × 10^-27 kg. It lets atomic and molecular masses be written as manageable numbers.

Related tools

• Kg to Lbs Converter — a dedicated tool with a full reference table.
• Lbs to Kg Converter — the same conversion in reverse.
• Volume Converter — for recipes and shipping, where both are needed.
• Torque Converter — where mass units turn into force units.

For the formula, the quick mental shortcuts and a printable chart, see our guide to converting kilograms to pounds.