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Molarity is the most common way chemists express concentration: moles of solute per litre of solution, written M or mol/L. It ties together three quantities — the mass of substance you weigh out, its molar mass, and the volume you dissolve it in.
Choose what you want to find, enter the values you know, and get the answer instantly.
Molarity Calculator: step-by-step worked example
- Solve for
- Molarity (from mass & volume)
- Molar mass (g/mol)
- 58.44
- Mass (g)
- 29.22
- Volume (L)
- 0.5
- 1
Moles of solute
n = m ÷ M
29.22 g ÷ 58.44 g/mol = 0.5 mol
- 2
Molarity
C = n ÷ V = m ÷ (M × V)
0.5 mol ÷ 0.5 L = 1 mol/L
- 3
In millimolar
mM = M × 1,000
1 × 1,000 = 1,000 mmol/L
- 0.25 L2 mol/L
- 0.5 L1 mol/L
- 1 L0.5 mol/L
- 2 L0.25 mol/L
Good to know: V is the FINAL solution volume in litres, not the water added: dissolve the solid, then top up to the mark in a volumetric flask. Example: 29.22 g NaCl (M = 58.44 g/mol) in 0.5 L gives 1 M.
Molarity Calculator — how it works
The molarity relation
Molarity links mass, molar mass and volume in one equation:
| Solve for | Formula |
|---|---|
| Molarity (M) | mass ÷ (molar mass × volume) |
| Mass (g) | molarity × molar mass × volume |
| Volume (L) | mass ÷ (molar mass × molarity) |
Volume is in litres, mass in grams and molar mass in g/mol, so molarity comes out in mol/L.
Getting the molar mass right
The molar mass is the sum of the atomic masses of every atom in the formula. For NaCl that's 22.99 (Na) + 35.45 (Cl) = 58.44 g/mol; for glucose C₆H₁₂O₆ it's 180.16 g/mol. A wrong molar mass is the single most common source of error, so double-check the formula before you start.
Molarity vs molality
Molarity (M) is moles per litre of *solution* and depends on temperature, because volume expands with heat. Molality (m) is moles per kilogram of *solvent* and does not. For most bench work at room temperature molarity is what you want; for precise thermodynamics, molality is preferred.
Where it helps
Preparing a solution of a known concentration, back-calculating how much you dissolved, or checking a lab protocol. To then dilute a stock solution to a lower concentration, use a dilution calculator.
Worked example
To make 0.5 L of a 2 mol/L NaCl solution, work in the "mass" direction: mass = molarity × molar mass × volume = 2 × 58.44 × 0.5 = 58.44 g. So you weigh out 58.44 g of sodium chloride and dissolve it to a final volume of 500 mL. If instead you dissolved 58.44 g in 1 L, the "molarity" direction gives 58.44 ÷ (58.44 × 1) = 1 mol/L.
Grams needed for 1 litre of common solutions
| Compound | 0.1 M | 0.5 M | 1 M |
|---|---|---|---|
| Sodium chloride (NaCl, 58.44 g/mol) | 5.84 g | 29.22 g | 58.44 g |
| Potassium chloride (KCl, 74.55 g/mol) | 7.46 g | 37.28 g | 74.55 g |
| Sodium hydroxide (NaOH, 40 g/mol) | 4 g | 20 g | 40 g |
| Calcium chloride (CaCl₂, 110.98 g/mol) | 11.1 g | 55.49 g | 110.98 g |
| Glucose (C₆H₁₂O₆, 180.16 g/mol) | 18.02 g | 90.08 g | 180.16 g |
| Sucrose (C₁₂H₂₂O₁₁, 342.3 g/mol) | 34.23 g | 171.15 g | 342.3 g |
| Tris base (C₄H₁₁NO₃, 121.14 g/mol) | 12.11 g | 60.57 g | 121.14 g |
| HEPES (C₈H₁₈N₂O₄S, 238.3 g/mol) | 23.83 g | 119.15 g | 238.3 g |
| EDTA (disodium) (C₁₀H₁₄N₂Na₂O₈, 336.21 g/mol) | 33.62 g | 168.11 g | 336.21 g |
| Monopotassium phosphate (KH₂PO₄, 136.09 g/mol) | 13.61 g | 68.05 g | 136.09 g |
Mass = molarity × volume × molar mass. For hydrated salts use the hydrate’s molar mass.
Frequently asked questions
What is molarity?+
Molarity is the concentration of a solution in moles of solute per litre of solution, written M or mol/L. A 1 M solution contains one mole of dissolved substance in every litre.
How do I calculate molarity from grams?+
First convert grams to moles by dividing by the molar mass, then divide by the volume in litres. The tool does both steps: molarity = mass ÷ (molar mass × volume).
How do I find the molar mass?+
Add the atomic masses of every atom in the chemical formula. NaCl = 22.99 + 35.45 = 58.44 g/mol. Enter this value in the molar mass field.
What is the difference between molarity and molality?+
Molarity is moles per litre of solution and changes slightly with temperature; molality is moles per kilogram of solvent and does not. Molarity (M) is the everyday lab measure.
How much solute do I need for a target molarity?+
Choose "Mass" mode: mass = molarity × molar mass × volume. For 0.5 L of 2 M NaCl that is 2 × 58.44 × 0.5 = 58.44 g.
About this page
- Publisher:
- Kalkoro — Teknolojig Bilişim Teknolojileri A.Ş., İstanbul
- Written by:
- Ahmet Tur — Editor (Math, date & time, unit conversion, physics & chemistry, everyday tools)
- Reviewed by:
- Kübra Yıldız — Editor
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