Molarity Calculator
Molarity from moles or from grams and molar mass, or the mass of solute you need to make a target concentration — volumes in mL, L or gallons, with the work shown.
Molarity Calculator: with the default inputs, molarity (mol/l) is 1.
Used in the mass → molarity mode.
Sum of the atomic masses in the formula. NaCl 58.44, glucose 180.16, NaOH 40.00, H₂SO₄ 98.08.
Used in the moles → molarity mode.
Total solution volume, not solvent added.
Used in the mass-needed mode.
- In millimolar (mM)
- 1,000
- Moles of solute (mol)
- 1
- Mass of solute
- 58.44 g
- Solved for
- M = 1 mol/L
Assumptions
- Volume is the final solution volume, measured after dissolving.
- The molar mass entered matches the substance actually weighed (hydrates included).
- Concentrations are formula-unit molarity, not ion molarity.
| Solute | Formula | Molar mass (g/mol) | Mass needed (g) |
|---|---|---|---|
| Sodium chloride | NaCl | 58.44 | 58.44 |
| Potassium chloride | KCl | 74.55 | 74.55 |
| Sodium hydroxide | NaOH | 40 | 40 |
| Potassium hydroxide | KOH | 56.11 | 56.11 |
| Sodium bicarbonate | NaHCO₃ | 84.01 | 84.01 |
| Hydrochloric acid | HCl | 36.46 | 36.46 |
| Sulfuric acid | H₂SO₄ | 98.08 | 98.08 |
| Glucose | C₆H₁₂O₆ | 180.16 | 180.16 |
| Sucrose | C₁₂H₂₂O₁₁ | 342.3 | 342.3 |
| Tris base | C₄H₁₁NO₃ | 121.14 | 121.14 |
| EDTA (free acid) | C₁₀H₁₆N₂O₈ | 292.24 | 292.24 |
| Calcium chloride | CaCl₂ | 110.98 | 110.98 |
| Magnesium sulfate | MgSO₄ | 120.37 | 120.37 |
| Ammonium chloride | NH₄Cl | 53.49 | 53.49 |
Molar masses are for the anhydrous compound. Dissolve, then make up to the final volume — molarity is moles per litre of solution, not per litre of solvent, and the two differ once the solution is concentrated.
How this is worked out
The formula
M = n ÷ V n = m ÷ Mᵣ M = molarity (mol/L, "molar", M) n = amount of solute (mol) V = volume of solution (L) m = mass of solute (g) Mᵣ = molar mass (g/mol) Mass needed: m = M × V × Mᵣ
Open How it’s calculated above to see this worked through with your own numbers.
What you enter
- What do you want to find?
- Choose one of 3 options.Molarity — from mass, molar mass & volume · Molarity — from moles & volume · Mass of solute — for a target molarity & volume
- Mass of solute
- Used in the mass → molarity mode.in g, mg, kg, oz, lb · 0 or more · defaults to 58.44
- Molar mass
- Sum of the atomic masses in the formula. NaCl 58.44, glucose 180.16, NaOH 40.00, H₂SO₄ 98.08.0 or more · defaults to 58.44
- Moles of solute
- Used in the moles → molarity mode.0 or more · defaults to 0.5
- Volume of solution
- Total solution volume, not solvent added.in L, mL, gal, fl oz, cup · 0 or more · defaults to 1
- Target molarity
- Used in the mass-needed mode.0 or more · defaults to 0.1
What you get back
- Molarity (mol/L)main answer
- In millimolar (mM)
- Moles of solute (mol)
- Mass of solute
- Solved for
What this assumes
- Volume is the final solution volume, measured after dissolving.
- The molar mass entered matches the substance actually weighed (hydrates included).
- Concentrations are formula-unit molarity, not ion molarity.
About this calculator
Molarity is moles of solute per liter of solution — the concentration unit chemistry runs on, because reactions happen between numbers of molecules, not grams. This calculator does the three jobs that come up at the bench and in homework: convert a weighed mass into molarity, convert moles into molarity, and — most usefully — tell you how many grams to weigh out to make a given volume of a target concentration.
How to use it
Enter the molar mass of your solute (add up the atomic masses from the periodic table; for hydrates include the water). Volumes can be in mL or L; masses in g or mg. The result is in mol/L with a millimolar conversion for biology-scale concentrations. The Solve for tool works backwards on any output, such as the volume that brings a fixed mass to 0.1 M.
Things that trip people up
- Volume of solution, not solvent. Dissolving 58.44 g of NaCl in 1 L of water gives slightly more than 1 L, so the result is slightly under 1 M. To make exactly 1 M, dissolve the salt in less water, then fill to the 1 L mark of a volumetric flask.
- Hydrates. CuSO₄·5H₂O has a molar mass of 249.7 g/mol, not the 159.6 of anhydrous CuSO₄. Weighing the hydrate with the anhydrous molar mass gives a solution 36% too dilute.
- Molarity vs. molality. Molality is moles per kilogram of solvent and doesn't change with temperature; molarity does, because the solution expands. For precise work at varying temperature, or freezing-point calculations, use molality.
- Ions vs. formula units. 1 M CaCl₂ contains 1 M Ca²⁺ and 2 M Cl⁻. Molarity counts formula units unless stated otherwise.
Reading the results
Moles of solute is the bridge quantity: it is what stoichiometry uses. Mass of solute in the moles mode assumes the molar mass you entered. For a 1 M target this tells you directly what to weigh; the millimolar line is the same number ×1,000.
Frequently asked questions
▸What is the formula for molarity?
Molarity = moles of solute ÷ liters of solution. If you start from mass, first divide grams by the molar mass (g/mol) to get moles.
▸How do I make a 1 M solution?
Weigh out one molar mass in grams (58.44 g for NaCl), dissolve it in somewhat less than 1 L of water, then add water to reach exactly 1.000 L of total solution. Use the mass-needed mode for other volumes and concentrations.
▸What is the difference between molarity and molality?
Molarity is moles per liter of solution and depends on temperature; molality is moles per kilogram of solvent and does not. For dilute aqueous solutions at room temperature the two are numerically close.
▸How do I convert molarity to grams per liter?
Multiply by the molar mass. A 0.5 M solution of NaCl (58.44 g/mol) contains 29.22 g of NaCl per liter.
▸What does mM mean?
Millimolar — one thousandth of a mole per liter. Blood glucose of 5 mM is 0.005 mol/L, about 0.9 g/L.
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