400 g to kg

400 g = 0.4 kg

Divide the gram value by 1,000 — the prefix kilo- means exactly one thousand. So 400 g ÷ 1,000 = 0.4 kg.

Multiply by 1,000, the inverse operation: 0.4 kg × 1,000 = 400 g. Converting in both directions is the quickest check that the figure is right.

Because kilo- stands for 10³, so one kilogram holds 1,000 grams. Moving the point by one or two places instead is the usual slip and makes the answer 100 or 10 times too large.