Molarity Calculator
Calculate molarity with personalized inputs and reference ranges for healthy values.
Step-by-Step
Common Compounds
What Is Molarity?
Molarity (M) measures the concentration of a solution as moles of solute per liter of solution. A 1 M sodium chloride solution contains 1 mole of NaCl (58.44 grams) dissolved in enough water to make exactly 1 liter of total solution. Molarity is the most commonly used concentration unit in chemistry because it directly relates to the number of molecules present, making stoichiometric calculations straightforward. This calculator converts between molarity, mass, volume, and molecular weight.
How to Calculate Molarity
Molarity = moles of solute / liters of solution. To find moles, divide the mass of solute (in grams) by its molecular weight (in g/mol). If you dissolve 5.85 grams of NaCl (molecular weight 58.44 g/mol) in water to make 500 mL of solution: moles = 5.85 / 58.44 = 0.10 mol. Molarity = 0.10 / 0.50 L = 0.20 M. Enter any combination of known values in the calculator above to find the unknown.
Preparing Solutions in the Lab
To prepare a specific molar solution, first calculate the required mass of solute: mass = molarity × volume (in liters) × molecular weight. For 250 mL of 0.5 M glucose (MW 180.16 g/mol): mass = 0.5 × 0.25 × 180.16 = 22.52 grams. Dissolve 22.52 grams of glucose in some water, then add water to bring the total volume to exactly 250 mL. Use a volumetric flask for accurate final volume. The key is that molarity is based on final solution volume, not the volume of solvent added.
Concentration Units Compared
Molarity is the default, but four other units show up often enough to know the difference.
| Unit | Definition | Best For |
|---|---|---|
| Molarity (M) | Moles solute per liter of solution | General lab work, stoichiometry |
| Molality (m) | Moles solute per kg of solvent | Temperature-sensitive work, freezing point |
| Normality (N) | Reactive equivalents per liter | Acid-base and redox titrations |
| w/v % | Grams solute per 100 mL solution | Clinical and pharmacy solutions |
| ppm | Parts per million by mass | Trace concentrations, water quality |
Molality wins where temperature changes, because mass does not expand or contract the way volume does. For everything tied to balanced equations, molarity is the working unit.
Molarity vs Other Concentration Units
Molality (m) uses moles per kilogram of solvent and is temperature-independent because mass does not change with temperature (volume does). Normality (N) considers the number of reactive equivalents and is used for acid-base and redox reactions. Weight/volume percentage (w/v%) expresses grams of solute per 100 mL of solution. Parts per million (ppm) is used for trace concentrations. Each unit serves a different purpose. Molarity dominates general chemistry lab work because it connects directly to balanced equations and stoichiometry.
Frequently asked questions
What is molarity?
How do I calculate molarity from grams?
What is the difference between molarity and molality?
How do I prepare a molar solution?
Why is final volume important, not solvent volume?
What does 0.1 M mean?
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