Which of these units is used to measure mass?

The SI unit of mass is the kilogram (kg). The kilogram 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⋅m2⋅s−1, where the meter and the second are defined in terms of c and ΔνCs. Among the SI base units, the kilogram (kg) is the only one whose name and symbol, for historical reasons, include a prefix. "Kilo" is the SI prefix for 1000 or 103. Names and symbols for decimal multiples and submultiples of the unit of mass are formed by attaching prefix names to the unit name "gram," and prefix symbols to the unit symbol "g."

Source: NIST