Molarity Calculator (Solution Concentration)

Calculate molar concentration, required solute mass, or solution volume using molecular weight formulas.

Reviewed for Mathematical Accuracy Last updated: 2026

How to Calculate Molarity and Prepare Chemical Solutions

Molarity (symbol M) is the standard measurement of chemical concentration in analytical chemistry, biochemistry, and pharmaceutical science. It expresses the number of moles of solute dissolved in one liter of total solution (mol/L). This free online molarity calculator helps students and lab technicians calculate concentration, solute mass, or volume without manual arithmetic errors.

Enter Solute Molar Mass: Input the formula weight of your chemical compound in grams per mole (g/mol). For example, sodium chloride (NaCl) is 58.44 g/mol.
Input Two Known Values: Enter any two of Mass (g), Volume (mL), or Molarity (mol/L).
View Solved Value: The tool automatically computes the third parameter. If you need to prepare 500 mL of a 0.5 M solution, entering volume and molarity reveals the exact grams to weigh on an analytical balance.
Reset Calculator: Click Clear All to clear all input values and start a new chemical preparation calculation.

The Molarity Formula (M = mol / L)

Molarity connects laboratory mass measurements with microscopic particle counts via Avogadro's constant (6.022 × 10²³ particles per mole):

Calculation Goal	Primary Formula	Units Required
Calculate Molarity (M)	M = (Mass / Molar Mass) / (Volume in L)	Mass in g, Volume in L, Result in mol/L
Calculate Solute Mass (g)	Mass = Molarity × (Volume in L) × Molar Mass	M in mol/L, Volume in L, Result in grams
Calculate Volume (L)	Volume = (Mass / Molar Mass) / Molarity	Mass in g, M in mol/L, Result in liters
Stock Solution Dilution	M1 × V1 = M2 × V2	M1, M2 in matching units; V1, V2 in matching units

How to Calculate Moles from Mass and Molar Mass

To determine the number of moles of a chemical solute, divide its measured mass in grams by its molar mass in grams per mole: Moles = Mass (g) / Molar Mass (g/mol). For instance, 10 grams of table salt (NaCl, molar mass 58.44 g/mol) contains exactly 0.1711 moles. Once you know the moles of solute, dividing by the solution volume in liters yields the molar concentration.

Solution Concentration Metrics Compared

Laboratories utilize different concentration scales depending on experimental conditions and temperature sensitivity:

Molarity (M): Defined as moles of solute per liter of solution. Standard for stoichiometric reactions, buffer preparation, and spectroscopy. Sensitive to temperature because liquid volume expands with heat.
Molality (m): Defined as moles of solute per kilogram of solvent. Preferred for thermodynamic studies, boiling point elevation, and freezing point depression because mass is temperature-independent.
Mass Concentration (g/L or mg/mL): Direct mass per volume, often used in enzyme assays, protein quantification, and pharmacology.
Percentage Concentration (% w/v): Grams of solute per 100 mL of solution. Common in medical saline solutions (such as 0.9% normal saline).

Preparing Dilutions: The M1V1 = M2V2 Equation

When creating working solutions from concentrated commercial stocks, the dilution formula conserves total moles of solute:

Problem: Prepare 500 mL of a 0.2 M hydrochloric acid (HCl) solution from a concentrated 2.0 M stock.
Rearrange Formula: V1 = (M2 × V2) / M1.
Calculate Stock Volume: V1 = (0.2 M × 500 mL) / 2.0 M = 50 mL.
Procedure: Measure 50 mL of 2.0 M HCl stock, add to roughly 400 mL of deionized water in a volumetric flask, then add water up to the 500 mL calibration mark. Always add acid to water, never water to acid.

Common Chemical Solutes & Molar Masses

Standard molecular weights for laboratory compounds frequently used with this calculator:

Sodium Chloride (NaCl): 58.44 g/mol
Sodium Hydroxide (NaOH): 40.00 g/mol
Hydrochloric Acid (HCl): 36.46 g/mol
Glucose (C6H12O6): 180.16 g/mol
Tris Base (C4H11NO3): 121.14 g/mol
Copper(II) Sulfate Pentahydrate (CuSO4·5H2O): 249.68 g/mol

Example: Calculating the Molarity of NaCl

Example 1 (Finding Concentration): Dissolve 10 grams of NaCl (58.44 g/mol) in water to make 500 mL of saline solution.

Moles of NaCl: 10 g / 58.44 g/mol = 0.1711 mol.
Volume in Liters: 500 mL / 1000 = 0.500 L.
Molarity: 0.1711 mol / 0.500 L = 0.3422 mol/L (0.342 M).

Example 2 (Finding Solute Mass): Determine how many grams of sodium hydroxide (NaOH, 40.00 g/mol) are needed to make 250 mL of a 0.1 M solution.

Moles needed: 0.1 mol/L × 0.250 L = 0.025 mol.
Mass needed: 0.025 mol × 40.00 g/mol = 1.000 gram.

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Frequently Asked Questions

How do I find the molar mass of a chemical compound?

Sum the standard atomic weights of every atom in the molecular formula using a periodic table. Molar mass is also printed on commercial reagent bottle labels and Safety Data Sheets (SDS).

Why is solution volume entered in milliliters while molarity is moles per liter?

Laboratory glassware such as volumetric flasks and graduated cylinders are calibrated in milliliters (mL). This calculator automatically divides milliliters by 1000 to convert into liters for molarity calculations.

What is the key difference between molarity and molality?

Molarity (M) measures moles of solute per liter of total solution, which fluctuates slightly with thermal expansion. Molality (m) measures moles of solute per kilogram of pure solvent, which remains constant across temperature changes.

How do I calculate stock solution dilutions?

Use the standard dilution equation M1 × V1 = M2 × V2, where M1 and V1 represent the concentration and volume of the stock solution, and M2 and V2 represent the final diluted working solution.

How should hydrated compounds be handled in molarity calculations?

Include the molecular mass of bound water molecules in your molar mass. For instance, copper sulfate pentahydrate (CuSO4·5H2O) has a molar mass of approximately 249.68 g/mol, compared to 159.61 g/mol for anhydrous copper sulfate.

Does this tool adjust for non-ideal solution contraction?

The calculator applies standard stoichiometry based on final total solution volume. For precise analytical work, always dissolve solute in partial solvent first, then dilute up to the volumetric calibration mark.

What is the formula for molarity?

Molarity (M) is calculated by dividing the number of moles of solute by the volume of the solution in liters. The formula is M = moles / Liters.

How do you find moles if you have mass?

To find the number of moles, divide the mass of the substance (in grams) by its molar mass (in g/mol).