Mass to Molarity Calculator
Enter your solute mass, molar mass, and final solution volume to calculate concentration in mol/L (M).
What is molarity?
Molarity is one of the most common concentration units in chemistry. It tells you how many moles of solute are present in one liter of solution. The unit is written as M, which is shorthand for mol/L.
If you already know the mass of a compound in grams, you can convert that mass to moles using the compound’s molar mass, then divide by final solution volume in liters. That is exactly what this mass to molarity calculator does.
Mass to molarity formula
The full conversion is:
M = (mass / molar mass) / volume(L)
- mass in grams (g)
- molar mass in grams per mole (g/mol)
- volume in liters (L)
If your volume is in mL, convert first: volume(L) = volume(mL) / 1000.
How to use this calculator
Step 1: Enter solute mass
This is the amount of chemical you weighed on the balance, in grams.
Step 2: Enter molar mass
Look up the molar mass from a periodic table or reagent label. For example, sodium chloride (NaCl) has a molar mass of 58.44 g/mol.
Step 3: Enter final volume
Use the total final volume of the prepared solution, not the amount of solvent you started with. Choose L, mL, or µL as needed.
Step 4: Add purity if needed
If your reagent is less than 100% pure, enter purity percent. The calculator adjusts effective mass automatically.
Worked example
Suppose you dissolve 5.84 g NaCl and make the final volume up to 500 mL.
- Molar mass of NaCl = 58.44 g/mol
- Moles = 5.84 / 58.44 = 0.0999 mol
- Volume = 500 mL = 0.500 L
- Molarity = 0.0999 / 0.500 = 0.200 M
This is a classic preparation for a 0.2 M sodium chloride solution.
Common molar masses for quick reference
| Compound | Formula | Molar Mass (g/mol) |
|---|---|---|
| Sodium chloride | NaCl | 58.44 |
| Potassium chloride | KCl | 74.55 |
| Glucose | C6H12O6 | 180.16 |
| Sulfuric acid | H2SO4 | 98.08 |
| Sodium hydroxide | NaOH | 40.00 |
Tips to avoid concentration errors
- Always use final solution volume, not solvent volume.
- Confirm units before calculating (mL vs L mistakes are very common).
- Check purity for hygroscopic or technical-grade chemicals.
- Use enough significant figures in intermediate steps.
- Label all prepared solutions with concentration, date, and initials.
FAQ
Is molarity the same as molality?
No. Molarity is moles per liter of solution. Molality is moles per kilogram of solvent.
Can I calculate from mg instead of g?
Yes, but convert first: mg / 1000 = g. Then use grams in the calculator.
What if my volume is in microliters?
Select µL in the volume unit menu. The calculator converts to liters automatically.
Final thoughts
A reliable mass to molarity conversion is essential for lab work, analytical chemistry, biology protocols, and classroom solution prep. Use this calculator to speed up your workflow and reduce unit-conversion mistakes. For critical experiments, always verify values with your SOP and lab supervisor.