Ounces to kilograms (oz to kg)

One ounce is exactly 0.0283495231 kilograms. That is a definition rather than a measurement: the imperial and US customary units were fixed against metric ones by the 1959 international yard and pound agreement, so this factor does not drift and will not be revised.

Worked through: 12 oz x 0.0283495231 = 0.340194 kg.

Going the other way, one kilogram is 35.27396195 ounces.

For mental arithmetic: Divide by 35.3.

One ounce is exactly 0.028349523125 kilograms, and the digits are exact because the pound was fixed at exactly 0.45359237 kg in 1959 and an ounce is a sixteenth of it. Two cautions. This is the avoirdupois ounce; a troy ounce, used for precious metals, is 31.103 grams rather than 28.35, so gold quoted per ounce is per a 10% heavier ounce. And a fluid ounce is a volume, not a mass. They share a name because a fluid ounce of water weighs about an ounce, which is true enough for water and false for everything else.

Precision is worth matching to the input. A measurement given as 1 oz carries one or two significant figures, and reporting its conversion to six implies a precision the original never had.