Molarity Calculator
Solve M = n ÷ V for concentration, moles or volume, then find exactly how many grams of solute to weigh for the solution you need.
M = n ÷ V
Solve for
M
Molarity
M
1 sig figs: 0.3
≡
Same value in
250,000 µM · 250,000,000 nM · 250 mol/m³
- Rearrange: M = n ÷ V
- Substitute: n = 0.125 mol, V = 500 mL (converted to SI units first).
- Result: M = 0.25 M, rounded to 1 significant figures because the least precise input has 1.
Grams to weigh for a solution
m
Mass of NaCl to weigh
g
0.125 mol × 58.44 g/mol
Stuck on the question behind this number?
Ask the StemCalc tutor. It explains the method step by step. Answers are AI-generated, so check them against your notes.
0/1500
Molarity in the lab
Molarity is the concentration unit you meet first because it connects directly to volumes you can measure with a pipette or burette: moles = molarity × litres. That one rearrangement drives titration calculations, dilutions and solution stoichiometry.
A common slip is forgetting to convert millilitres to litres. 0.125 mol in 500 mL is 0.125 ÷ 0.500 = 0.250 M, not 0.125 ÷ 500. The unit menus above convert for you.
To make a weaker solution from a stock bottle, use the dilution calculator.
Frequently asked questions
What is the molarity formula?
Molarity M = moles of solute ÷ litres of solution. Its unit is mol/L, written M. A 1 M solution has one mole of solute in every litre of solution.
How do I calculate molarity from grams?
Convert grams to moles with the molar mass first (n = m ÷ M), then divide by the volume in litres. 5.85 g NaCl (58.44 g/mol) in 250 mL: 0.100 mol ÷ 0.250 L = 0.400 M.
Is the volume of solvent or of solution?
Of the finished solution. In the lab you dissolve the solute in less solvent, then top up to the mark in a volumetric flask.
What is the difference between molarity and molality?
Molarity is moles per litre of solution and changes slightly with temperature; molality (m) is moles per kilogram of solvent and does not. Colligative-property problems (boiling point elevation) use molality.
How do I make a solution of a given molarity?
Use the “grams to weigh” panel: enter the formula, target concentration and flask volume. Weigh that mass, dissolve it in about half the final volume, transfer to a volumetric flask and fill to the line.