What this calculator does
Percent, permille, ppm, ppb and ppt are all the same kind of thing: a fraction expressed against a different power of ten. Percent is per hundred, permille per thousand, ppm per million, and so on down. Once that is clear the conversions are just moving a decimal point.
The one worth committing to memory is that 1% is 10,000 ppm, because it is the conversion most often got wrong by a factor of a hundred. Going the other way, 500 ppm is 0.05%, which looks surprisingly small written that way and is a large part of why water and air quality figures are quoted in ppm rather than as percentages.
The formula
Every unit is expressed as a plain fraction of the whole, and the conversion multiplies by the source factor and divides by the target. Percent is 0.01, permille 0.001, ppm one millionth, ppb one billionth and ppt one trillionth. No physical assumptions are involved, so the same conversion applies whether the fraction is by mass, by volume or by count, provided both figures use the same basis.
| Term | Meaning |
|---|---|
| Percent (%) | Parts per hundred, a factor of 0.01. |
| Permille (‰) | Parts per thousand, a factor of 0.001. Common in salinity and in some financial contexts. |
| ppm | Parts per million. The usual unit for trace concentrations in water, air and soil. |
| ppb | Parts per billion, a thousandth of a ppm, used where ppm would be an awkward decimal. |
The inputs explained
| Field | What to enter |
|---|---|
| Value | The concentration value. |
| From | The unit it is currently in. |
| To | The unit you want the answer in. |
When to use it
Reading a water quality report
Limits are set in ppm or mg/L and results sometimes reported as percentages, and the factor of 10,000 between them is easy to lose.
Converting a trace contaminant figure
Air quality and soil contamination figures run from ppm down to ppt, and putting two reports on the same scale is the only way to compare them.
Checking a dilution or formulation
Active ingredient concentrations are quoted as percentages on labels and as ppm in technical data, so converting confirms the two describe the same product.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
What is one of each concentration unit in ppm?
One unit of each kind, converted to parts per million.
| From | In ppm |
|---|---|
| Whole fraction (1 = everything) | 1,000,000 ppm |
| Percent | 10,000 ppm |
| Permille | 1,000 ppm |
| Part per billion | 0.001 ppm |
Converting 500 ppm to the other concentration units
A concentration of 500 parts per million expressed in each of the other units.
| To | Result |
|---|---|
| Percent | 0.05 percent |
| Permille | 0.5 permille |
| Whole fraction | 0.0005 fraction |
| Parts per billion | 500,000 ppb |
Questions
How many ppm in 1 percent?
10,000. Percent is parts per hundred and ppm is parts per million, so the factor between them is 10,000. This is the single most commonly mistaken conversion on this page, usually by confusing it with the 1,000 that separates ppm from permille.
Is ppm the same as mg/L?
For dilute water solutions, near enough, because a litre of water weighs about a kilogram and a milligram is a millionth of that. It is an approximation that relies on the solution being mostly water at ordinary temperature, and it does not hold for other solvents or for gases.
Does ppm measure mass or volume?
Either, and the report should say which. Parts per million by mass and by volume give different numbers for the same sample unless the densities happen to match. Air concentrations are usually by volume and water concentrations usually by mass.
What is a permille?
Parts per thousand, written with the ‰ symbol. It sits between percent and ppm and is used where percent would give awkward decimals, most commonly for seawater salinity and for blood alcohol concentration in some countries.
For diluting a concentrate to a target strength, see the volume converter for the underlying volume arithmetic. For mass fractions specifically, see the mass converter.