PPM to Molarity Calculator

Convert parts per million (ppm) to molarity (M) and vice versa for chemical solutions with molar mass and density inputs.

g/mol

Molecular weight of the solute

ppm
M
kg/L

Solution density in kg/L

Results

Converted Concentration

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Concentration (mg/L)

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Formula Used

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Frequently Asked Questions

What is the difference between ppm and molarity?

PPM (parts per million) represents the mass ratio of solute to solution (typically mg/L for dilute solutions), while molarity (M) measures the number of moles of solute per liter of solution. Molarity considers the molecular weight of the substance.

How do I convert ppm to molarity?

To convert ppm to molarity, use the formula: M = (ppm × ρ / 1000) / Mᵣ, where ρ is solution density (kg/L) and Mᵣ is molar mass (g/mol). For dilute aqueous solutions, ρ ≈ 1.000 kg/L.

When should I use custom density instead of assuming water?

Use custom density for concentrated solutions, non-aqueous solvents, or when working with solutions that have significantly different densities than water (1.000 kg/L). This provides more accurate conversions.

Why is molar mass important in the conversion?

Molar mass converts between mass-based concentration (ppm) and mole-based concentration (molarity). Different substances have different molecular weights, so the same ppm value will result in different molarities.

What does 1 ppm equal in mg/L?

For dilute aqueous solutions, 1 ppm approximately equals 1 mg/L. This approximation holds when the solution density is close to that of pure water (1.000 kg/L).

How accurate is the water density assumption?

The water density assumption (ρ = 1.000 kg/L) is very accurate for dilute solutions (typically <1000 ppm). For more concentrated solutions, using the actual solution density improves accuracy.

Can I convert molarity back to ppm?

Yes, use the reverse formula: ppm = (1000 × M × Mᵣ) / ρ. Enter your molarity value and the calculator will compute the equivalent ppm concentration using the same molar mass and density parameters.

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