PPM ⇄ Molarity Calculator

Use this PPM to Molarity Calculator to convert between ppm, ppb, molarity, millimolar, micromolar, and nanomolar concentrations. Enter the concentration and the molar mass of the substance.

PPM to Molarity Formula

For a dilute aqueous solution:

1 ppm ≈ 1 mg/L

Molarity (M) = ppm ÷ (1,000 × molar mass)

The molar mass must be entered in grams per mole (g/mol).

For ppb:

Molarity (M) = ppb ÷ (1,000,000 × molar mass)

To convert molarity back to ppm:

ppm ≈ molarity × molar mass × 1,000

Worked Example

Suppose a dilute sodium chloride solution has a concentration of 200 ppm. The molar mass of sodium chloride is 58.44 g/mol.

Molarity = 200 ÷ (1,000 × 58.44)

Molarity ≈ 0.00342 M

To convert the result to millimolar:

0.00342 × 1,000 = 3.42 mM

Therefore, 200 ppm of sodium chloride is approximately 0.00342 M or 3.42 mM.

Important Notes

• The approximation 1 ppm ≈ 1 mg/L applies to dilute water-based solutions whose density is close to that of water.
• It may not be valid for gases, solids, concentrated solutions, or non-aqueous solvents.
• Use the molar mass of the exact substance or ion represented by the ppm value.
• For example, ppm of chloride requires the molar mass of chloride, while ppm of sodium chloride requires the molar mass of sodium chloride.

Sources

• OpenStax Chemistry 2e — Molarity
• U.S. Geological Survey — Water-Quality Concentration Units