Math
PPM Calculator
Convert parts-per-million between ppm, ppb, ppt, percent, mg/L, ug/L, and gas-phase mg/m^3 at 25 C and 1 atm using molecular weight.
PPM Calculator
Enter a value in any unit (ppm, ppb, ppt, %, mg/L, ug/L, mg/m^3) and see all the others.
Used only for the gas-phase mg/m^3 row at 25 C and 1 atm.
Equivalent concentrations
5 ppm
ppb
5,000
ppt
5,000,000
percent
0.0005 %
mg/L (aqueous)
5 mg/L
ug/L (aqueous)
5,000 ug/L
mg/m^3 (gas)
Enter MW to compute
Frequently Asked Questions about the PPM Calculator
What does ppm mean and how do I convert it to percent?
Parts per million (ppm) measures how many units of a substance exist per million units of mixture. To convert to percent, divide by 10,000: 1 ppm equals 0.0001 percent, and 1 percent equals 10,000 ppm. The same value is also 1,000 ppb (parts per billion) and 1,000,000 ppt (parts per trillion).
Why does the calculator treat 1 ppm as 1 mg/L for water?
For dilute aqueous solutions, the density is close to 1.0 g/mL, so 1 mg of solute in 1 L of solution is roughly 1 ppm by mass. This shortcut breaks down for concentrated brines, organic solvents, or anything far from water density, where you should use the mass-to-mass mode instead.
How do I convert mg/m^3 of a gas to ppm by volume?
Use ppm_v = (mg/m^3) x 24.45 / MW, where 24.45 L/mol is the molar volume of an ideal gas at 25 C and 1 atm, and MW is the molecular weight in g/mol. For example, 50 mg/m^3 of carbon monoxide (MW 28.01) works out to about 43.65 ppm by volume.
When should I use the mass / mass mode?
Pick mass / mass any time you know the weighed mass of solute and total solution, especially for solids, sludges, soils, or non-aqueous mixtures. The calculator returns ppm = (solute mass / solution mass) x 1,000,000, and both inputs must share the same unit (grams with grams, milligrams with milligrams).
Why is molecular weight required for the gas conversion?
Gas-phase ppm is a volume ratio, while mg/m^3 is a mass per unit volume. Bridging the two needs the molar volume of an ideal gas (24.45 L/mol at 25 C, 1 atm) and the molecular weight of the specific gas. Without MW, the calculator cannot tell whether 1 ppm of, say, CO and SO2 share the same mg/m^3 (they do not).