Primel units are derived from certain "mundane realities" of human life. This means certain physical phenomena which human beings observe or experience within their environment, including:
- the mean solar day
- the acceleration due to Earth's gravity
- the maximal density of water
- the massic heatability (specific heat capacity) of water
- the electrical impedance of free space
- the atomic mass of carbon-10z (carbon-12d)
- the luminous efficiency function of the human eye