Concentration Converter
Convert a solution concentration between percent (w/v and w/w), ppm, ppb, mg/L, g/L and molar units (mol/L, mM, µM, nM). Enter the solute's molecular weight for molar units and the solution density for mass-percent units; every other unit is shown at once.
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Needed for mol/L, mM, µM and nM. NaCl = 58.44 g/mol.
Needed for % w/w, ppm and ppb. Use 1 for dilute water solutions.
How to use the Concentration Converter
- Enter the concentration and pick the unit it is in.
- Pick the unit you want to convert to.
- Add the molecular weight (g/mol) if either unit is molar: tap a preset or type it from the label or a molar mass calculator.
- Set the solution density for % w/w, ppm or ppb (1 g/mL for dilute water solutions).
- Press Convert to see the result, the steps and the value in every other unit.
How concentration units convert
The converter first turns your value into grams of solute per litre of solution (g/L), then into the target unit. Three kinds of units are involved:
| Kind | Units | To g/L | Needs |
|---|---|---|---|
| Mass per volume | % w/v, g/L, mg/mL, mg/L, µg/mL, µg/L | % w/v × 10; mg/L ÷ 1000; µg/L ÷ 1,000,000 | nothing extra |
| Mass per mass | % w/w, ppm, ppb | fraction × density (g/mL) × 1000 | solution density |
| Amount per volume | mol/L, mM, µM, nM | mol/L × molecular weight | molecular weight |
Example: convert 2.5 % w/w sucrose (342.30 g/mol) with density 1.008 g/mL to mM. 2.5 % w/w = 0.025 × 1008 g/L = 25.2 g/L; 25.2 ÷ 342.30 = 0.07362 mol/L = 73.62 mM.
Quick reference
| Equivalence | Notes |
|---|---|
| 1 g/L = 1 mg/mL = 1,000 mg/L | Always true |
| 1 mg/L = 1 µg/mL = 1,000 µg/L | Always true |
| 1 % w/v = 10 g/L = 10,000 mg/L | Always true |
| 1 ppm ≈ 1 mg/L, 1 ppb ≈ 1 µg/L | Only when density ≈ 1 g/mL |
| 1 % w/w = 10,000 ppm | Both are mass ratios |
| 1 M = 1,000 mM = 1,000,000 µM | Always true |
| mg/L = mM × MW (g/mol); µg/L = µM × MW | Handy shortcut for molar ⇄ mass units |
Tips
- Hydrates matter. Use the molecular weight of the form you actually weigh: CuSO₄ is 159.61 g/mol but CuSO₄·5H₂O is 249.69 g/mol.
- "As CaCO₃" or "as N": water reports often express hardness or nitrate as an equivalent compound or element. Use that reference compound's molecular weight (100.09 for CaCO₃, 14.007 for N).
- % v/v (volume percent, used for alcohol) is not covered here because it depends on the pure solute's density, not the solution's.
- Densities change with temperature. For precise work, use the density measured at your working temperature.
Frequently asked questions
How do I convert mg/L to mol/L?
Divide by 1,000 to get g/L, then divide by the molecular weight: mol/L = (mg/L ÷ 1000) ÷ MW. For example, 500 mg/L of NaCl (58.44 g/mol) is 0.5 ÷ 58.44 = 0.00856 mol/L, or 8.56 mM.
How do I convert ppm to molarity?
For a dilute water solution, ppm ≈ mg/L, so molarity = ppm ÷ 1000 ÷ MW. 120 ppm of calcium carbonate (100.09 g/mol) is 1.2 mM. For denser solutions, multiply ppm by the density in g/mL first.
What is the difference between % w/v and % w/w?
% w/v is grams of solute per 100 mL of solution. % w/w is grams of solute per 100 g of solution. They are equal only when the solution density is 1 g/mL; otherwise % w/v = % w/w × density.
Is 1 ppm the same as 1 mg/L?
Only approximately, for dilute aqueous solutions whose density is close to 1 g/mL. ppm is a mass ratio (mg per kg of solution), while mg/L is mass per volume. For seawater or concentrated solutions, use the actual density.
How do I convert mM to mg/mL?
Multiply millimolar by the molecular weight and divide by 1,000: mg/mL = mM × MW ÷ 1000. A 10 mM glucose solution (180.16 g/mol) is 1.80 mg/mL.
What is a 1% solution in molarity?
A 1% w/v solution has 10 g per litre, so molarity = 10 ÷ MW. For sodium chloride that is 10 ÷ 58.44 = 0.171 mol/L (171 mM).
Why does the tool need the density?
Mass-per-mass units such as % w/w, ppm and ppb tell you grams of solute per gram of solution. To compare them with per-litre units you need to know how many grams one litre of the solution weighs, which is the density × 1,000.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.