# Molarity Calculator URL: https://speedycalculator.com/calculators/chemistry/molarity/ Last updated: 2026-10-30 > The molarity calculator gives the molar concentration of a solution in mol/L from the mass of solute, its molar mass and the solution volume, plus the moles, mass concentration and percentages. Type a target molarity into the result to find how many grams to weigh out. ## Inputs - Mass of solute (g, mg, µg, kg, oz, lb) - Molar mass of solute (g/mol, kg/mol, Da (u), kDa) — Default: sodium hydroxide NaOH. Use the formula mass including any water of crystallisation. - Volume of solution (L, mL, µL, m³, dm³, cm³, US gal, fl oz (US)) - Density of the solution (optional) (g/mL, g/cm³, kg/m³, kg/L, lb/ft³) — Only needed for mass percent and molality. About 1.00 g/mL for dilute water solutions; 1 M NaOH is about 1.04 g/mL. ## Results - Amount of substance - Molarity - Mass concentration - Weight per volume - Number of solute particles - Mass percent (w/w) - Molality ## Formula ``` n = m ÷ M · c = n ÷ V = m ÷ (M × V) · m = c × V × M Mass concentration ρ* = m ÷ V = c × M · molality b = n ÷ (ρ_solution × V − m) ``` ## Explanation Molarity, or amount concentration, is the number of moles of solute in one litre of solution, written mol/L or simply M. A 1 M sodium chloride solution contains 58.44 g of NaCl in every litre of finished solution. Because chemical reactions happen between particles in fixed mole ratios, molarity is the most practical way to express concentration in the lab: multiply it by a volume and you immediately know how many moles you have dispensed. To prepare a solution, you work backwards: decide the molarity and volume you need, calculate the mass (m = c × V × M), weigh it out, dissolve it in less solvent than the final volume, transfer it to a volumetric flask and top up to the mark. Note that the volume is that of the final solution, not of the water you add – dissolving a solid usually changes the volume a little. Besides molarity, this calculator reports the amount in moles, the mass concentration (g/L, the same as mg/mL), the weight-per-volume percentage, and – if you enter the solution density – the mass percent and the molality, which is the concentration per kilogram of solvent. ### How to use the Molarity Calculator - **Mass of solute** - **Molar mass of solute** — Default: sodium hydroxide NaOH. Use the formula mass including any water of crystallisation. - **Volume of solution** - **Density of the solution (optional)** — Only needed for mass percent and molality. About 1.00 g/mL for dilute water solutions; 1 M NaOH is about 1.04 g/mL. - Want to work backwards? Type a value into **Molarity** and **Mass of solute** is calculated for you. Results update as you type, every field has its own unit menu, and everything is calculated in your browser. ### How it works Divide the mass of solute by its molar mass to get moles, then divide by the solution volume in litres. To find the mass needed for a target concentration, type the molarity into the result – the calculator solves backwards for the mass. Mass percent and molality use the solution density to find the mass of the whole solution. ### Worked example 10 g of sodium hydroxide (NaOH, M = 39.997 g/mol) is dissolved and made up to 250 mL. n = 10 ÷ 39.997 = 0.2500 mol and c = 0.2500 ÷ 0.250 L = 1.000 M. The mass concentration is 10 g ÷ 0.25 L = 40 g/L (4% w/v). With a solution density of 1.04 g/mL the 250 mL weighs 260 g, so the solution is 10 ÷ 260 = 3.85% NaOH by mass and its molality is 0.2500 mol ÷ 0.250 kg of water = 1.000 mol/kg. ### Making a solution step by step - Choose the molarity and the final volume you need. - Type the molarity into the result to get the mass (m = c × V × M). - Weigh the solute and dissolve it in roughly two thirds of the final volume of solvent. - Transfer quantitatively to a volumetric flask, rinsing the beaker into it. - Make up to the mark at room temperature and mix by inverting the stoppered flask. ### Inputs explained FieldWhat to enterMass of soluteUnits: g, mg, µg, kg, oz, lbMolar mass of soluteUnits: g/mol, kg/mol, Da (u), kDa. Default: sodium hydroxide NaOH. Use the formula mass including any water of crystallisation.Volume of solutionUnits: L, mL, µL, m³, dm³, cm³ …Density of the solution (optional)Units: g/mL, g/cm³, kg/m³, kg/L, lb/ft³. Only needed for mass percent and molality. About 1.00 g/mL for dilute water solutions; 1 M NaOH is about 1.04 g/mL. ### What each result means - **Amount of substance** = [Mass of solute] ÷ [Molar mass of solute] - **Molarity** = [Amount of substance] ÷ [Volume of solution] - **Mass concentration** = [Mass of solute] ÷ [Volume of solution] - **Weight per volume** = [Mass of solute]÷([Volume of solution]×1000)×100 - **Number of solute particles** = [Amount of substance]×6.02214076e+23 - **Mass percent (w/w)** = ([Mass of solute]÷([Density of the solution (optional)]×1000×[Volume of solution]))×100 - **Molality** = [Amount of substance]÷(([Density of the solution (optional)]×1000×[Volume of solution] - [Mass of solute])÷1000) ### Example values How the main result changes when **Mass of solute** changes and everything else stays at the example values above: Mass of solute (g)Molarity (mol/L (M))50.57.50.7501101.000112.51.2501151.5001202.0002 ## Worked example Inputs — Mass of solute: 10 g; Molar mass of solute: 39.997 g/mol; Volume of solution: 0.25 L; Density of the solution (optional): 1.04 g/mL. Results — Amount of substance = 0.250019 mol; **Molarity = 1.000075 mol/L (M)**; Mass concentration = 40 g/L; Weight per volume = 4 % w/v; Number of solute particles = 1.5056e23; Mass percent (w/w) = 3.8462 %; Molality = 1.000075 mol/kg. ## Key terms - **Molarity (amount concentration)**: Moles of solute per litre of solution, mol/L. - **Molar mass**: Mass of one mole of a substance, g/mol. - **Mass concentration**: Mass of solute per volume of solution, g/L. - **Volumetric flask**: Flask calibrated to hold one exact volume at the mark, used to make standard solutions. ## FAQ **What is molarity?** The number of moles of solute per litre of solution (mol/L, M). A 2 M solution has 2 mol of solute in every litre. **How do I calculate molarity from grams?** Divide the mass by the molar mass to get moles, then divide by the volume in litres. 5 g of HCl (36.46 g/mol) in 1.2 L: 0.1371 mol ÷ 1.2 L = 0.114 M. **How many grams do I need for a 0.1 M solution?** m = c × V × M. For 500 mL of 0.1 M NaCl: 0.1 × 0.5 × 58.44 = 2.922 g. Type 0.1 into the molarity result and the calculator finds the mass for you. **Is the volume that of the solvent or the solution?** The solution. Dissolve the solute in part of the solvent, then make up to the final volume in a volumetric flask. **What is the difference between M, mM and µM?** 1 M = 1 mol/L, 1 mM = 0.001 mol/L and 1 µM = 10⁻⁶ mol/L. Use the unit menu on the result to switch. **Does molarity change with temperature?** Slightly: the solution expands when warmed, so the same moles occupy a larger volume. Water expands about 0.26% between 20 and 30 °C. **How do I convert molarity to g/L?** Multiply by the molar mass: 0.5 M glucose is 0.5 × 180.16 = 90.08 g/L. **What is the molarity of pure water?** About 55.3 M (997 g/L ÷ 18.015 g/mol at 25 °C). **Can I work backwards from the result?** Yes. Type the result you want into Molarity and the calculator finds the matching mass of solute. ## Sources - [IUPAC Compendium of Chemical Terminology (Gold Book)](https://goldbook.iupac.org/) - [OpenStax – Chemistry 2e](https://openstax.org/details/books/chemistry-2e) - [IUPAC Commission on Isotopic Abundances and Atomic Weights – Standard atomic weights](https://www.ciaaw.org/atomic-weights.htm)