What would be better though? 1kg is 1kg, regardless of temperature, pressure and volume. A litre, gallon, cc, all need clarification with respect to something e

What would be better though? 1kg is 1kg, regardless of temperature, pressure and volume. A litre, gallon, cc, all need clarification with respect to something else. You could use moles, but for a given compound, mass is just a more accessible, yet equally accurate, scaled value.