The link between mass and capacity (or volume) is density.
The unit of mass is the kilogram and the unit of volume is the cubic metre.
The density of pure water is 1000 kilograms per cubic metre.
The litre is a derived unit which is a 1000th of a cubic metre, so 1 litre of pure water has a mass of 1 kilogram.
The density of steel is about 8000 kilograms per cubic metre. so 1 kg of steel would be ~ 125 cm³.
