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Analytical chemistry · Trace concentration

ppm, ppb & Molarity Concentration Converter

Convert between molarity, mmol/L, mg/L, µg/L, ppm, ppb, and mass percent using explicit solute molar mass and solution density.

Formula shown Runs locally Reviewed Aug 11, 2026
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Equation guide

Homogeneous solution with explicit solute molar mass and solution density

Mass fraction

ppm = mg/kgppb = µg/kg

Amount concentration

c = β/M

Density connection

β = wρ
Analytical concentration

Connect amount, mass, and trace concentration

Inputs and displayed values use at most three decimal places. ppm and ppb are treated as mass fractions (mg/kg and µg/kg), so density is required when converting to volume-based units.

ppm ⇄ mol/L

Choose the concentration basis, solute molar mass, and solution density.

Using the model

Symbols, assumptions and limitations

Interpretation notes

ppm and ppb are mass fractions in this calculator. Converting them to volume-based concentrations requires solution density, while converting mass concentration to amount concentration also requires solute molar mass. Every conversion must imply a solute mass fraction from 0% through 100%. The model assumes a homogeneous solution and analytical concentration, not chemical speciation or activity.

Worked examples

See the method in practice

01

Dilute sodium chloride in water

For a water-like density, 100 ppm NaCl is close to 100 mg/L, but its molarity additionally depends on the 58.44 g/mol molar mass.

02

A non-aqueous matrix

In ethanol, ppm and mg/L are not numerically equal because the solution density is substantially below 1 kg/L.

Questions

Frequently asked

Is 1 ppm always 1 mg/L?

No. One ppm by mass is 1 mg/kg. It is approximately 1 mg/L only when solution density is close to 1 kg/L.

Why is molar mass required?

Molarity counts moles per litre, while ppm, ppb, and mass concentration describe mass. Molar mass connects solute mass and amount.

Does this calculate ionic speciation?

No. It converts the analytical amount of the selected solute. Dissociation, complex formation, acid–base equilibria, and activity corrections require separate chemical models.

Sources & review

Equations and examples are checked against the references below. Results are educational and should be independently verified for safety-critical work.

IUPAC Gold Book — amount concentration NIST — SI units and prefixes

Written by the STEM Hub editorial team · Reviewed August 11, 2026 · Review methodology