percent
ConcentrationDimensionlessexact by definition
The percent is one part in a hundred and serves as the base unit of this dimensionless concentration type, so its factor of 1 is exact. It is the most common way to express a concentration outside the laboratory, but it is also the most ambiguous, because a percentage can be by mass, by volume, or mass per volume.
Watch out: State the basis. In water and chemical work, % w/w is grams per 100 g of solution, % v/v is millilitres per 100 mL, and % w/v is grams per 100 mL. A 12.5 percent sodium hypochlorite solution is quoted by trade convention as available chlorine by weight, while a 50 percent glycol mix is almost always by volume. The three bases can differ by tens of percent for the same physical solution.
| 1 (Concentration) | 1 |
| 1 (Dimensionless) | 0.01 |
Percent is a dimensionless ratio expressed in hundredths, so 1 percent is exactly 0.01 as a plain ratio. It is a way of writing a number rather than a unit, which is why the conversion factor is exact by definition. The related forms are per mille at one thousandth, and parts per million at 1e-6.
One percent in every concentration unit
| 10,000,000,000 | part per trillion (ppt) | |
| 10,000,000,000 | nanogram per liter (ng/L) | |
| 10,000,000 | parts per billion (ppb) | convert → |
| 10,000,000 | microgram per liter (μg/L) | |
| 10,000 | parts per million (ppm) | convert → |
| 10,000 | part per million by volume (ppmv) | |
| 10,000 | milligram per kilogram (mg/kg) | |
| 10,000 | milligram per liter (mg/L) | |
| 584.18 | grain per US gallon (as CaCO₃) (gpg) | convert → |
| 10 | part per thousand (ppth) | |
| 10 | gram per liter (g/L) | |
| 1 | percent (%)this unit | |
| 1 | percent by weight (% w/w) | |
| 1 | percent by volume (% v/v) | |
| 1 | percent weight per volume (% w/v) | |
| 0.01 | fraction (0–1) (fraction) |
One percent in every dimensionless unit
| 10,000,000,000 | part per trillion (ppt) | |
| 10,000,000 | part per billion (ppb) | |
| 10,000 | part per million (ppm) | |
| 1,000 | per cent mille (pcm) | |
| 100 | basis point (bp) | |
| 10 | per mille (per mille) | |
| 1 | percent (%)this unit | |
| 0.01 | ratio (—) |