Molarity & concentration converter: M, mM, mg/mL, %, ppm
Chemists express solution composition in several units. Molarity (mol/L of solution) is common in volumetric work. Molality (mol/kg of solvent) is preferred when temperature changes matter. Mass percent and ppm appear in analytical and environmental contexts. Converting among them requires the solute’s molar mass and, for most conversions, the solution density.
The Molarity & Concentration Converter takes one known concentration plus molar mass (from a formula or a typed value) and density, then reports molarity in M, mM, and μM, plus g/L, g/mL, mg/mL, mass percent, ppm, and molality on a 1.00 L solution basis. Density-aware examples (saline, glucose, ethanol) help connect classroom molarity problems to everyday mg/mL and g↔mL conversions.
For dilute aqueous solutions, density ≈ 1.00 g/mL is a standard classroom approximation. Concentrated acids, bases, and syrups need a measured or tabulated density or the conversion will be off.
- Molarity M = moles solute / liters solution; 1 M = 1000 mM = 10⁶ μM
- Molality m = moles solute / kilograms solvent
- Mass % and ppm need density to relate mass of solute to volume of solution
Formulas you will actually use
For 1.00 L of solution with density ρ (g/mL) and solute molar mass M (g/mol):
Mass of solution ≈ 1000ρ grams
Mass of solute (g) = (molarity) × M
1 M = 1000 mM = 10⁶ μM
Mass % = (mass solute / mass solution) × 100%
ppm (mass) = (mass solute / mass solution) × 10⁶
Molality = moles solute / kg solvent
kg solvent = (mass solution − mass solute) / 1000- ppm here is mass ppm (mg/kg). For very dilute water solutions this is nearly mg/L.
- If solute mass exceeds solution mass, the inputs are physically inconsistent.
Step-by-step example: 0.100 M NaCl with density 1.00 g/mL
Convert 0.100 M aqueous NaCl (M ≈ 58.44 g/mol, ρ = 1.00 g/mL) into g/L, mass percent, ppm, and molality.
- g/L = 0.100 × 58.44 = 5.844 g/L.
- In 1.00 L, solution mass ≈ 1000 g; solute = 5.844 g.
- Mass % ≈ (5.844 / 1000) × 100 = 0.584%.
- ppm ≈ 5844.
- kg solvent ≈ 0.994 kg; molality ≈ 0.100 / 0.994 ≈ 0.101 mol/kg.
Enter NaCl, density 1.00, molarity 0.100 in the Molarity & Concentration Converter and compare the table of results.
Frequently asked questions
How do I convert concentration to molarity?
Choose the unit you already know (mM, μM, g/L, mg/mL, mass %, ppm, or molality), enter the value plus a formula or molar mass and density, and read molarity in mol/L. The converter always reports M, mM, and μM together (1 M = 1000 mM = 10⁶ μM).
How do I convert mg/mL to molarity?
mg/mL is numerically the same as g/L (1 mg/mL = 1 g/L). Choose the mg/mL unit, enter the value and the solute formula (or molar mass), then read molarity: M = (mg/mL) / molar mass. Example: 5.844 mg/mL NaCl (58.44 g/mol) is 0.100 M.
How do I convert millimolar to molar?
1 M = 1000 mM = 10⁶ μM, so divide mM by 1000 to get M (100 mM = 0.100 M). Choose Millimolar or Micromolar as the known unit and read molarity in the results table; the reverse is multiply.
How do I convert ppm to percent?
Mass percent = ppm / 10,000 because 1% = 10,000 ppm. The converter reports both from the same 1.00 L basis once you enter a formula (or molar mass) and density.
When is molality better than molarity?
Molality does not change with temperature because it is based on solvent mass, not solution volume. Colligative-property problems usually use molality.
Why do I need density?
Molarity is per liter of solution, while mass percent and molality are mass-based. Density links volume of solution to its mass so those families of units can be connected.
What if I do not know the formula?
Leave the formula blank and type the molar mass in g/mol directly. The converter only needs M for mole ↔ mass links.
References & further reading
Standards bodies, university open courseware, and peer-reviewed references that align with the methods used on this page.
Keep learning with more calculators and study guides on Online Science Tools.