part per billion
Dimensionlessexact by definition
One part per billion is exactly 1e-9 of the whole, one thousandth of a part per million. It is the unit of trace contaminant regulation: the US action level for lead in drinking water is 15 ppb, and ozone and benzene limits in air are set in the low tens. The factor is exact by definition.
Watch out: The billion here is the short-scale thousand million. Older British and continental European texts used the long-scale billion of a million million, so a very old document reading ppb may mean what is now called ppt. The ambiguity is why the SI recommends writing the power of ten instead.
| 1 | 1.0000000e-09 |
One part per billion in every dimensionless unit
| 1,000 | part per trillion (ppt) | |
| 1 | part per billion (ppb)this unit | |
| 0.001 | part per million (ppm) | |
| 0.0001 | per cent mille (pcm) | |
| 0.00001 | basis point (bp) | |
| 0.000001 | per mille (per mille) | |
| 1.00000e-07 | percent (%) | |
| 1.00000e-09 | ratio (—) |
Solvers that use dimensionless