Molarity Calculator — Calculate Concentration, Moles & Volume
Use the molarity formula M = n / V to solve for concentration (mol/L), moles of solute, or volume of solution. Enter any two values and this calculator instantly computes the third. The built-in mass-to-moles helper converts grams to moles using molar mass, with one-click presets for common lab compounds including NaCl, NaOH, HCl, H₂SO₄, and glucose.
Molarity Calculator
Mass to Moles Helper
Convert mass (grams) to moles using molar mass, then auto-fill the moles field above.
Frequently Asked Questions
What is molarity?
Molarity (M) is a measure of solution concentration defined as the number of moles of solute dissolved in one liter of solution. The unit is mol/L, often written as M. For example, a 1 M NaCl solution contains 1 mole of sodium chloride (58.44 g) dissolved in enough water to make 1 liter of total solution. Molarity is the most common concentration unit used in chemistry laboratories.
How do you calculate molarity?
Molarity is calculated with the formula M = n / V, where M is molarity in mol/L, n is the number of moles of solute, and V is the volume of the solution in liters. For example, if you dissolve 0.5 mol of NaOH in 2 liters of water, the molarity is 0.5 / 2 = 0.25 mol/L. If you start with grams instead of moles, first convert: moles = mass (g) / molar mass (g/mol).
How do you find moles from molarity and volume?
To find moles, rearrange the molarity formula to n = M × V. Multiply the molarity (in mol/L) by the volume (in liters). For example, to find how many moles are in 250 mL of a 0.1 M HCl solution: convert 250 mL to 0.25 L, then n = 0.1 × 0.25 = 0.025 mol. This is useful for calculating how much solute to weigh out when preparing a solution.
How do you calculate volume from molarity and moles?
Rearrange the molarity equation to V = n / M. Divide the number of moles by the molarity. For example, if you need 0.05 mol of sulfuric acid from a 2 M stock solution, the volume needed is V = 0.05 / 2 = 0.025 L, or 25 mL. This calculation is fundamental to solution preparation and dilution procedures.
How do you convert grams to moles?
Convert grams to moles using n = m / Mr, where m is the mass in grams and Mr is the molar mass in g/mol. The molar mass equals the sum of atomic masses of all atoms in the compound's formula, which you can look up on a periodic table. For example, NaCl has a molar mass of 22.99 (Na) + 35.45 (Cl) = 58.44 g/mol. So 100 g of NaCl contains 100 / 58.44 ≈ 1.711 moles.
What is the difference between molarity and molality?
Molarity (M) measures moles of solute per liter of solution and varies with temperature because liquid volume changes with heat. Molality (m) measures moles of solute per kilogram of solvent and is temperature-independent. For dilute aqueous solutions near room temperature, the two values are nearly equal. Molarity is used most often in volumetric analysis and reagent preparation; molality is preferred for colligative properties like boiling point elevation and freezing point depression.
What units does molarity use?
Molarity is expressed in units of mol/L, also written as M or molar. Millimolar (mM) equals 0.001 mol/L, and micromolar (μM) equals 0.000001 mol/L. In biochemistry, concentrations are often expressed in millimolar or micromolar since biological molecules are present at very low concentrations. The liter is the standard unit for volume in molarity calculations, so volumes in milliliters must be divided by 1000 before using the formula.
How is molarity used in lab calculations?
Molarity is central to laboratory solution preparation, titrations, spectrophotometric assays, and reaction stoichiometry. When preparing a standard solution, you calculate the mass of solute needed (mass = M × V × molar mass). In titrations, you use M₁V₁ = M₂V₂ to determine unknown concentrations. Beer-Lambert law uses molarity to relate absorbance to concentration. Reaction yield calculations use molarity to determine limiting reagents and theoretical yields from solution reactions.
Molarity Formula
Molarity (M) is the most common unit for expressing solution concentration in chemistry and biology. It describes the number of moles of solute dissolved per liter of solution. This calculator solves for any one of the three related variables — molarity, moles, or volume — when the other two are known.
How to Calculate Molarity
M = n / V
Rearranging the formula gives:
- n = M × V — to find moles when molarity and volume are known
- V = n / M — to find volume when moles and molarity are known
How to Use This Calculator
- Select what you want to solve for: Molarity, Moles, or Volume.
- Enter the two known values in the input fields.
- The result appears instantly — all three values are shown together.
- Optionally use the Mass to Moles Helper if you know the mass and molar mass of your solute instead of the number of moles directly.
Mass to Moles Conversion
In most lab scenarios you weigh out a solid on a balance, so you have mass in grams rather than moles. Convert grams to moles using:
n = m / Mr
n = moles | m = mass (g) | Mr = molar mass (g/mol)
The helper section in the calculator lets you enter the mass and select from common compounds (or type any molar mass), then click "Use this value" to auto-fill the moles field.
Common Molar Masses
The molar mass of a compound equals the sum of the atomic masses of all atoms in one formula unit.
| Compound | Formula | Molar Mass (g/mol) |
|---|---|---|
| Sodium chloride | NaCl | 58.44 |
| Sodium hydroxide | NaOH | 40.00 |
| Hydrochloric acid | HCl | 36.46 |
| Sulfuric acid | H₂SO₄ | 98.08 |
| Glucose | C₆H₁₂O₆ | 180.16 |
| Water | H₂O | 18.015 |
| Potassium chloride | KCl | 74.55 |
| Calcium chloride | CaCl₂ | 110.98 |
| Acetic acid | CH₃COOH | 60.05 |
| Ethanol | C₂H₅OH | 46.07 |
Molarity vs Molality
Molarity and molality are both measures of concentration but they differ in what the denominator refers to:
Molarity (M)
Moles of solute per liter of solution. Depends on temperature because liquid volume expands with heat. Most common in volumetric analysis and lab reagent preparation.
M = n / Vsolution
Molality (m)
Moles of solute per kilogram of solvent. Temperature-independent because mass does not change with temperature. Preferred in boiling point elevation and freezing point depression calculations.
m = n / kgsolvent
For dilute aqueous solutions at room temperature, molarity and molality are numerically similar because the density of water is approximately 1 kg/L.
Related Tools
- Dilution Calculator — Calculate C₁V₁ = C₂V₂ dilutions. Find the volume or concentration after diluting a stock solution.
- mEq to mg Calculator — Convert between milliequivalents and milligrams for electrolytes and ionic compounds.