What is the si unit of mass?

The SI unit of mass is kilogram (kg).

The SI unit for mass is the kilogram

The kilogram, symbol kg, is the SI unit of mass. It is defined by taking the fixed numerical value of the Planck constant h to be 6.62607015×10^-34 when expressed in the unit J⋅s, which is equal to kg⋅m^2 s^-1, where the metre and the second are defined in terms of c and ΔνCs.