Molarity Calculator
Solution concentration in mol/L from grams, molar mass, and volume.
What it does
Molarity counts how many moles of solute sit in each liter of solution. It drives stoichiometry, titrations, and buffer recipes: reactions care about molecule counts, and molarity converts weighable grams into those counts per volume.
The tool above takes solute grams, molar mass, and final liters. It returns moles, molarity, and grams per liter together so weighing and pipetting read off one pass.
The default dissolves 58.44 g of table salt (molar mass 58.44) into 1 L: exactly 1 mol for a 1 M solution at 58.44 g/L. Halving the salt to 29.22 g halves everything to 0.5 mol and 0.5 M.
Definitions follow the IUPAC Gold Book amount of substance entries with the same worked patterns taught in Khan Academy chemistry units. Both fix molarity as moles per liter of finished solution, not per liter of solvent poured.
How to use
- Enter the solute grams weighed on the balance.
- Enter the molar mass from the formula weights.
- Enter the final solution volume in liters.
- Read molarity first for the reaction math.
- Use moles and g/L for weighing the next batch.
Formula
- moles
- Molecule count in Avogadro units.
- molar mass
- Grams per mole from atomic weights.
- liters
- Finished solution volume, not solvent added.
Volume means after dissolving and topping up in a volumetric flask. Dumping solute into a full liter overshoots because the solid displaces liquid.
Worked example
Example: 58.44 g NaCl in 1 L
Grams 58.44, molar mass 58.44, volume 1 L.
- Moles: 58.44 / 58.44 = 1 mol.
- Molarity: 1 / 1 = 1 M.
- Mass conc: 58.44 / 1 = 58.44 g/L.
- Bench path: dissolve in about 800 mL water, then top up to 1 L.
- Tool shows 1 M, 1 mol, 58.44 g/L.
Reference table
| Solute | Molar mass | Grams for 1 M |
|---|---|---|
| NaCl | 58.44 g/mol | 58.44 g |
| Glucose | 180.16 g/mol | 180.16 g |
| CaCO3 | 100.09 g/mol | 100.09 g |
| NaOH | 40.00 g/mol | 40.00 g |
Limits
- Ideal dissolving assumed; volumes shift slightly at high conc.
- Purity matters: technical grade weighs include impurities.
- Hydrates need their water counted in molar mass.
- Temperature moves volumes a little; state 20 or 25 C for records.
Common mistakes
- Dividing by milliliters instead of liters.
- Topping solvent to a liter instead of solution to a liter.
- Using atomic number instead of atomic weight.
- Forgetting hydrate water in the molar mass.
- Reading M as molality (per kg solvent) by accident.
Try it yourself
Quick checks. Answers sit tucked under each question.
29.22 g NaCl in 1 L?
0.5 mol, 0.5 M, 29.22 g/L.
10 g NaOH (40.00) in 0.5 L?
0.25 mol / 0.5 L = 0.5 M.
Moles in 90.08 g glucose?
90.08 / 180.16 = 0.5 mol.
Questions
What is 1 molar?
One mole per liter of finished solution. For NaCl that is 58.44 g topped to 1 L.
Molarity vs molality?
Molarity divides by solution liters, molality by solvent kilos. Dilute water work barely differs.
How do I make 0.5 M?
Halve the 1 M grams or double the volume. For NaCl: 29.22 g to 1 L.
Why top up instead of adding 1 L?
The solid takes space, so adding a full liter overshoots the mark and dilutes below target.
Do hydrates change the math?
Yes. Use the hydrate molar mass including waters, since part of the weighed grams is water.
What does M mean on a bottle?
mol/L of the named solute at the stated temperature.