Concentration Calculator — Molarity from Mass and Volume
Enter the mass of solute, its molar mass, and the total solution volume to find the molarity in mol/L (M). The calculator also shows the amount of substance in moles and the mass concentration in g/L.
g
g/mol
L
Moles of solute per litre of solution (M)
- 1
Moles of solute
20 ÷ 58.44 = 0.34223 mol - 2
Molarity = moles ÷ volume
0.34223 ÷ 0.5 = 0.6845
How does this calculator work?
Molarity c = mass / (M_r × V): divide the mass of solute (g) by the molar mass (g/mol) to get moles, then divide by the solution volume in litres. For 20 g of NaCl (M_r = 58.44) dissolved to 0.5 L: c = 20 / (58.44 × 0.5) ≈ 0.684 mol/L.
Formula
How this is calculated
Molarity (also called molar concentration) is the amount of solute in moles per litre of solution: c = n/V. To find n from a measured mass, divide by the molar mass M_r (g/mol): n = mass/M_r. Combining these gives c = mass / (M_r × V), which is the formula this calculator uses.
Molarity is the most commonly used concentration unit in chemistry because it directly relates to the number of reacting particles. Common lab solutions range from very dilute (< 0.01 M) to highly concentrated (e.g. 12 M hydrochloric acid, ≈18 M sulfuric acid). The mass fraction (w/w %) approximation shown assumes the solvent density is 1 g/mL (water at room temperature) — this is not accurate for organic solvents or at high concentrations.
Note: molarity depends on the total volume of solution, not just the volume of solvent. When preparing a solution of a given molarity, dissolve the solute in a small amount of solvent first, then make up to the final volume in a volumetric flask — do not add the solvent volume to the solute volume, as volumes are not always additive.
Frequently asked questions
Molarity (M) is moles of solute per litre of solution (volume-based, changes with temperature). Molality (m) is moles of solute per kilogram of solvent (mass-based, temperature-independent). For dilute aqueous solutions at 25°C the two are approximately equal, but they diverge for concentrated solutions or non-aqueous solvents.
Add the atomic masses of all atoms in the chemical formula. Atomic masses are on the periodic table (e.g. Na = 22.99, Cl = 35.45 → NaCl = 58.44 g/mol). For biological molecules, the molar mass is usually given in the product specification in g/mol or Da (daltons, numerically identical).
Weigh 58.44 g of NaCl (1 mole). Dissolve it in about 800 mL of distilled water, then transfer to a 1 L volumetric flask and make up to the 1 L mark. Do not simply add 1 L of water to the salt — the final volume must be 1 L, not the solvent volume.
Also known as
TG we-Calculate Editorial Team. (2026). Concentration Calculator — Molarity from Mass and Volume [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/concentration-calculator
TG we-Calculate Editorial Team. "Concentration Calculator — Molarity from Mass and Volume." TG we-Calculate. 2026. https://we-calculate.com/calculator/concentration-calculator.
TG we-Calculate Editorial Team, "Concentration Calculator — Molarity from Mass and Volume," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/concentration-calculator
@misc{wecalculate_concentration_calculator, title = {Concentration Calculator — Molarity from Mass and Volume}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/concentration-calculator}}, year = {2026}, note = {TG we-Calculate} }
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