Dalton's Law of Partial Pressures Calculator

Dalton's Law states that the total pressure of a mixture of non-reacting gases equals the sum of the partial pressures of each gas. If oxygen, nitrogen, and argon each push on a container wall, the pressure you measure is the sum of those individual contributions.

A partial pressure is the pressure a single gas in a mixture would exert if it alone occupied the whole volume at the same temperature. It reflects how much of that gas is present relative to the rest of the mixture.

Each gas's mole fraction equals its partial pressure divided by the total pressure. Because the fractions are shares of the same whole, they always add up to 1. In partial-pressures mode the tool computes each fraction this way.

Any consistent unit works, such as atm, kPa, bar, psi, or mmHg, as long as every value uses the same one. The calculator never converts units, so the total and partial pressures come back in whatever unit you typed in.

Mole fractions describe each gas's share of the whole mixture, so they must total 1. In total mode the tool checks the sum within a tolerance of 0.000001 and shows an error if the fractions do not add up, for example 0.2 and 0.7.

Yes. Enter as many comma-separated values as your mixture has components. The results table lists one row per gas as Gas 1, Gas 2, and so on, in the order you typed them.

A component of exactly 0 is allowed, and it contributes a mole fraction of 0. The only hard limit is that the total pressure must be greater than zero, so at least one gas must have a positive pressure.

Every output is rounded to six decimal places. For clean inputs like 2, 3, and 5 the fractions come out as tidy values such as 0.2, 0.3, and 0.5, while less even mixtures may show a longer decimal.

The calculation runs in your browser, so nothing you type is uploaded. There is also a JSON API for the same engine if you want to script it: post partialPressures for one mode, or totalPressure plus moleFractions for the other.