Enter a value once and read it in every other unit of that category at the same time. Includes the Korean traditional units — 평, 돈, 근, 되 — that ordinary conversion tables leave out.
Most unit conversions are a single multiplication, which is why the interesting ones are the units where that is not true. Temperature has an offset as well as a scale, so 0°C is not zero anything. And several units still in daily Korean use are traditional rather than metric: 평 is 400/121 m² — 3.3058, the exact legal definition rather than the rounded 3.3 that creeps into listings — 돈 is 3.75 g for gold, 냥 is 37.5 g and 근 is 600 g as a butcher uses it. Those are the numbers people actually search for and the ones a generic converter omits.
Conversions here go through a single base unit per category rather than a table of pair-to-pair factors, so converting inches to millimetres and back returns the number you started with instead of drifting a little further each round trip.
Rounded conversion factors are how a small error becomes a legal one. 평 is defined as 400/121 square metres — 3.30578..., not the 3.3 that appears in property listings — and over an apartment of 30 평 the difference is about a fifth of a square metre. The same applies to the traditional weights still in daily use: 돈 is exactly 3.75 grams, which matters when the thing being weighed is gold, and 근 is 600 grams for meat but 375 grams for vegetables and dried goods in some traditional markets, a distinction generic converters do not make.
Temperature is the conversion that cannot be done by multiplication, because its scales have different zero points as well as different sizes of degree. That is also why a temperature difference converts differently from a temperature: a rise of 10°C is a rise of 18°F, not 50°F. Kelvin shares the Celsius degree size and shifts the origin to absolute zero, which is why it takes no degree sign. Getting this wrong produces answers that are plausible enough to survive a glance, which is the dangerous kind.
Everything here converts through one base unit per category rather than through a table of pair-to-pair factors, and the reason is accumulated error. A direct inch-to-millimetre factor and a direct millimetre-to-inch factor that are each rounded separately will not return you to the value you started with, and a few round trips visibly drift. Going through a single canonical unit means one rounding rather than two, so converting out and back gives the number you began with.
Every factor is the exact defined value where one exists — an inch is exactly 25.4 mm, a pound exactly 0.45359237 kg, and 1 평 exactly 400/121 m². Results are rounded for display only; the copy button gives the full-precision figure.
200 mL, the metric cup used in Korean and Japanese recipes. US customary cups are about 237 mL, so an American recipe will be slightly under-measured if you use this one.
The unit historically differed by trade. Meat is sold by the 600 g 근, while fruit and vegetables commonly use 375 g. Both remain in everyday use, so confirm with the seller.