What this calculator does
Find out how strong a solution is, or how much of a substance to weigh out to make one. Molarity is the most common way to say how concentrated a solution is. The substance you dissolve is called the solute. Molarity counts how many moles of it are in each liter of finished solution. A mole is a set number of particles, like a "dozen" but far bigger. Molarity is written mol/L, or M for short. A 1 M salt (sodium chloride) solution holds one mole of NaCl, 58.44 g, in every liter.
The formula c = n ÷ V links three things: concentration, moles and volume. With a molar mass (the weight of one mole), it also links the mass of solute. Pick the one you want to find and enter the others. The most common lab use is finding the mass. It tells you how many grams to weigh out for the strength and volume you want.
Where it's used
Why this math matters outside the classroom:
- Saline solution. A lab tech making 1 L of 0.15 M sodium chloride weighs out 0.15 × 58.44 ≈ 8.77 g of salt.
- Titrations. Students in titration labs convert a measured volume of 0.1 M base into moles to find an acid's concentration.
- Working solutions. Researchers dilute 1 M stock solutions into millimolar working concentrations for cell culture and enzyme assays.
- Water testing. Water quality labs report dissolved substances as concentrations so readings from different samples can be compared.
Grade level and standards: Grades 10–11; Common Core State Standards for Mathematics HSA.CED.A.4. © Copyright 2010. National Governors Association Center for Best Practices and Council of Chief State School Officers. All rights reserved.
How to use it
- Choose what to find: molarity, moles of solute, mass of solute, or volume of solution.
- If you're finding molarity or volume, say how you know the solute: as a mass with its molar mass, or directly in moles.
- Enter the values you know and pick their units. Volumes can be µL, mL or L. Concentrations can be M, mM, µM or nM.
- Read the result and the steps. They show every unit change before the formula is used.
What the inputs mean
- Molar mass of solute
- The mass of one mole of the solute, in grams per mole (g/mol). For hydrated salts (crystals that hold water), use the molar mass of the form you're actually weighing.
- Molarity
- 1 M = 1 mol/L = 1,000 mM = 1,000,000 µM.
- Volume of solution
- This is the final volume of the whole solution, not the volume of water you start with. Dissolving a solid changes the volume a little. That's why labs fill solutions up to a marked line in a volumetric flask.
Formula and method
c = n ÷ V n = m ÷ M m = c × V × M V = n ÷ c
Here's what each letter means. c is molarity in moles per liter, and n is moles of solute. V is the volume of solution in liters. m is the mass of solute in grams, and M is its molar mass in grams per mole.
Every number you enter is first changed to moles, liters and grams. So a volume in mL is divided by 1,000, and a concentration in mM is divided by 1,000, before the formula is used.
Worked example
You need 250 mL of 0.25 M sodium chloride solution. How much NaCl (58.44 g/mol) should you weigh out?
- Convert the volume to liters: 250 mL × 0.001 = 0.25 L.
- Moles needed: n = 0.25 M × 0.25 L = 0.0625 mol.
- Mass: m = 0.0625 mol × 58.44 g/mol = 3.6525 g.
Result: Weigh 3.6525 g of NaCl, dissolve it, and make the solution up to 250 mL.
Understanding the result
A higher molarity means more solute particles in the same volume. Comparing molarities only makes sense for the same solute, or when you care about the number of particles rather than their weight.
For ionic compounds, such as salts that split into charged particles in water, molarity counts the whole compound. A 0.1 M CaCl2 solution is 0.1 M in calcium ions but 0.2 M in chloride ions.
Assumptions and limitations
- The volume is the total volume of solution after mixing.
- Unit changes use the exact metric prefixes (1 mL = 0.001 L, 1 mM = 0.001 M).
- Temperature effects on volume are ignored. Molarity changes slightly as a solution expands or shrinks with temperature.
- It doesn't allow for purity. If your chemical is 98% pure, divide the mass by 0.98.
- Molarity isn't the same as molality, which is moles per kilogram of solvent (the liquid you dissolve into). Use the molality calculator when you need a measure that doesn't change with temperature.
- It doesn't plan dilutions from a stronger stock solution. Use the dilution calculator for C1V1 = C2V2.
Frequently asked questions
What does 1 M mean?
One mole of solute in each liter of solution. For glucose (180.156 g/mol), a 1 M solution holds 180.156 g of glucose per liter.
How do I make a solution of a given molarity?
Multiply the molarity by the volume in liters to get moles. Then multiply by the molar mass to get grams. Dissolve that mass in less liquid than you need. Then add liquid up to the final volume and mix.
Why use the solution volume and not the solvent volume?
Molarity is measured per liter of finished solution. Adding a solid to 1 L of water usually gives slightly more than 1 L of solution. So if you measured only the water, your concentration would come out a little too high.
What is the difference between molarity and molality?
Molarity divides moles by liters of solution. Molality divides moles by kilograms of solvent. Molality doesn't change with temperature, which is why it's preferred for boiling and freezing point calculations.
How this calculator is checked
Method: Definition of amount concentration, c = n/V, with n = m/M. The calculation is covered by automated tests with known reference values and edge cases. Last updated 2026-10-18. Found a problem? Tell us.
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