# How Do You Convert Molarity to Ppm?

By Staff WriterLast Updated Mar 31, 2020 4:38:31 PM ET

For dilute solutions, convert molarity to ppm by multiplying the molarity by the molecular mass of the solute, then multiplying the result by 1000.

1. Ensure your solution is dilute

Molarity is a measure of number of molecules per unit volume, and ppm (parts per million) is a measure of proportion by mass. If the solution is dilute enough that adding the solute does not appreciably change the solution's volume or mass, you can perform this conversion. As a rule of thumb, once you get above 1,000 ppm, then parts per million is not the right unit of measurement.

2. Convert mol/L to g/L

Molarity is measured in terms of moles per liter (mol/L). Multiply this by the molecular mass of the solute in grams per mol (g/mol). The unit of moles will cancel, and you will be left with a measure of grams per liter (g/L).

3. Convert g/L to mg/L

Multiply your grams per liter (g/L) from the step above by the simple metric system conversion factor of 1000 milligrams per gram (1000 mg/g). The grams cancel, and the result is the concentration of solute in mg/L.

4. Change the final unit to ppm

There are one million milligrams in one kilogram. A liter of water weighs one kilogram. Therefore, 1 mg/L equals 1 ppm. Your answer in mg/L is your final answer in ppm.