Molarity Calculator
Calculate solution molarity, the mass needed, or a dilution.
Please note: Results come from idealised models that assume clean, standard conditions. Real measurements deviate, and published constants carry their own tolerances. Use these for study and estimation, not for engineering sign-off.
What the Molarity Calculator does
Molarity is the concentration of a solution in moles of solute per litre of solution. Converting a weighed mass into moles requires the molar mass, and diluting an existing solution keeps the moles fixed while the volume grows — the basis of M₁V₁ = M₂V₂.
Formula
M = n ÷ V(litres)n = mass ÷ molar massM₁V₁ = M₂V₂ (dilution)Solvent to add = V₂ − V₁
Inputs explained
| Input | Unit | Required | Notes |
|---|---|---|---|
| Calculate | one of 3 options | Yes | — |
| Mass of solute | number | In some modes | Shown Calculate is Molarity from mass and volume. |
| Mass of solute unit | one of 6 options | In some modes | Shown Calculate is Molarity from mass and volume. |
| Molar mass of the solute | g/mol | In some modes | NaCl is 58.44, glucose 180.16, water 18.02. Accepts more than 0. Shown Calculate is Molarity from mass and volume, or Calculate is Mass needed for a target molarity. |
| Solution volume | number | In some modes | Shown Calculate is Molarity from mass and volume, or Calculate is Mass needed for a target molarity. |
| Solution volume unit | one of 6 options | In some modes | Shown Calculate is Molarity from mass and volume, or Calculate is Mass needed for a target molarity. |
| Target molarity | mol/L | In some modes | Accepts more than 0. Shown Calculate is Mass needed for a target molarity. |
| Starting concentration (M₁) | mol/L | In some modes | Accepts 0 or more. Shown Calculate is Dilution (M₁V₁ = M₂V₂). |
| Starting volume (V₁) | number | In some modes | Shown Calculate is Dilution (M₁V₁ = M₂V₂). |
| Starting volume (V₁) unit | one of 6 options | In some modes | Shown Calculate is Dilution (M₁V₁ = M₂V₂). |
| Final concentration (M₂) | mol/L | In some modes | Accepts 0 or more. Shown Calculate is Dilution (M₁V₁ = M₂V₂). |
How to use it
- Choose Calculate.
- Fill in the remaining inputs the form shows for your choice.
- Select Calculate.
Worked example
Dissolving 58.44 g of sodium chloride to make 1 litre of solution.
- Mass
- 58.44 g
- Molar mass
- 58.44 g/mol
- Volume
- 1 L
n = 58.44 ÷ 58.44 = 1 mol, so M = 1 ÷ 1 = 1.0 mol/L — a one molar solution containing 6.022 × 10²³ formula units.
Frequently asked questions
What is the difference between molarity and molality?
Molarity is moles per litre of solution; molality is moles per kilogram of solvent. Molality is unaffected by temperature, which is why it is preferred for precise thermodynamic work.
Do I add solute to a litre of water?
No. Dissolve the solute in less water, then make the total volume up to one litre. Adding solute to a full litre gives a slightly larger volume and a weaker solution.