Convert ppm, Percent and Per Mille

Converter for the specification ppm, parts per million, in percent and per mille.

ppm can often be found as specification of low concentrations. 1 ppm means one part of one million, 1 percent is one part of one hundred and 1 per mille is one part of one thousand.

Please enter one value, the other two values will be calculated. One per mille corresponds to one thousand ppm, one percent is ten thousand ppm, ppm can also be referred to as millionth. Even lower is the less commonly used ppb, parts per billion; 1000 ppb = 1 ppm.

Just like percent, ppm can be used for continuous quantities, such as mass. However, it is often actually used for particles in the physical sense; this, of course, is also possible with percent and per mille.
The most common case in which ppm is used as a proportional unit is the proportion of carbon dioxide, CO₂, in the air. The pre-industrial value was 280 ppm, meaning that at that time, approximately 280 out of every million molecules in the air were carbon dioxide molecules. In 2024, this value rose to 425 ppm. The increase is largely due to the combustion of fossil fuels, i.e., coal, oil, and natural gas, and is the primary cause of human-induced climate change. This effect is based on the fact that gas molecules consisting of more than two atoms absorb infrared radiation, thus storing heat. Carbon dioxide is by far the most abundant such molecule in the Earth's atmosphere.
The mass share of CO₂ in the atmosphere is over half more than the share of particles, as the CO₂ molecule is more massive than the predominant nitrogen and oxygen molecules. It is 644 ppm, or 0.664 per mille, or 0.0664 percent.
The argument often used by climate change deniers that millionths are so small that they can't make a difference is simply physically unfounded and plain wrong. Concentrations in the ppm range can have noticeable effects in other areas as well, for example, in medicines and fragrances.