We use grams(g) and kilograms(kg) to measure mass (or weight).
We use centimetres(cm), metres(m) and kilometres(km) for length.
We use millilitres(ml) or litres(L) for capacity (how much liquid).
A chair weighs about 5 kilograms.
A pencil weighs about 20 grams.
A cup holds about 200 ml.
A bucket holds about 10 litres.