There are only two natural units: space and time.
All conventional units of measure can be converted to natural units. In the SI system:
- meters: s1/t0 = s, where one unit of space is approximately 45 nm in length. (note that "s" in natural units refers to "space," not "seconds.")
- kilograms: t3/s3
- seconds: t1/s0 = t, where one unit of time is approximately 152 attoseconds in duration.
Unit speed forms the datum of natural units, being s0/t0.