Weight Converter

Most weight units scale by a single fixed factor, which makes them easy to trust. A few carry more than one definition under the same name, and the difference is large enough to matter if you use the wrong one.

Troy weight is a separate system, not a variant

Gold, silver and gemstones are weighed in troy units, and a troy pound is not the same pound used for groceries. A troy pound is 12 troy ounces and comes to about 373 grams, lighter than the everyday avoirdupois pound at roughly 454 grams. The individual ounces run the other way: a troy ounce, at about 31.1 grams, is heavier than an avoirdupois ounce at about 28.35 grams. The pound gets lighter under troy rules while the ounce gets heavier, because troy divides its pound into 12 ounces instead of 16. A jeweler's quote and a kitchen scale can both say "ounces" and mean measurably different amounts.

There are three different tons

A metric tonne is 1,000 kilograms. A US short ton is 2,000 pounds, about 907 kilograms. A UK long ton is 2,240 pounds, about 1,016 kilograms. Shipping manifests, commodity prices and vehicle weight ratings each tend to favor a different one depending on the industry and country, and the three-way gap between short ton and long ton alone is over 10 percent, large enough to matter on any figure quoted without its specific unit named.

A scale reads force, and gravity is not perfectly constant

A bathroom or kitchen scale actually measures the force gravity exerts on an object, then reports it as if it were mass. Earth's gravity is slightly stronger near the poles and slightly weaker near the equator and at altitude, a spread of roughly half a percent across the planet's surface. The same physical mass will register a marginally different weight in Oslo than in Nairobi. It is far too small to notice on a kitchen scale, but it is the reason precision scientific and industrial scales are calibrated to the specific location they operate in rather than assumed universal.