Molarity Calculator

A solution labeled 1 M contains one mole of the stated solute entity in each liter of final solution. The identity matters: sodium chloride, a hydrate, a salt form, and an isotopically enriched material can have different molar masses even when their everyday names look related.

Molarity links amount of substance to final solution volume. It is often used to work backward from a target concentration, determine how much material to weigh, or check the concentration made from a known mass. The denominator is the completed solution volume after dissolution and adjustment, not simply the starting solvent volume.

Molarity

Amount of solute divided by final solution volume, commonly expressed in mol/L.

Molar mass

Mass of one mole of the stated chemical entity, expressed in g/mol.

As-weighed mass

The material placed on the balance before a purity adjustment.

Pure-solute mass

As-weighed mass multiplied by the declared mass-purity fraction.

Unit prefixes can hide large differences. One millimolar is 0.001 mol/L, one micromolar is 0.000001 mol/L, and one nanomolar is 0.000000001 mol/L. Converting every quantity to a consistent base before solving prevents a milliliter or milligram entry from being treated as liters or grams.

Molarity can change with temperature because solution volume changes. Material purity, hydration state, assay basis, and formula choice can also change the correct weighed mass. A clean calculation is therefore a check on stated quantities, not proof that the prepared solution meets a laboratory method.

Use the chemical form and purity specified by the protocol or certificate of analysis. For unusual isotopic composition, non-standard material, or a formula the supported notation cannot represent, use a protocol-approved manual molar mass.

How to Use This Tool:

Choose the missing quantity first; the calculator then asks only for a sufficient set of known quantities.

1. Set Solve for to molarity, amount of solute, as-weighed solute mass, final solution volume, or molar mass.
2. Choose the available Known quantities. Depending on the target, this is known moles, known mass with molar mass, or known molarity with final volume.
3. When molar mass is needed, select a supported Chemical formula or enter a Manual molar mass for the exact material form. Include hydrate or solvate notation when it changes composition.
4. Enter the quantities with their units. For mass-based paths, supply a purity greater than 0% and no more than 100%.
5. Check the solved quantity and the normalized evidence. If formula validation fails, correct capitalization, grouping, subscripts, or hydrate separators, or switch to a verified manual molar mass.

Interpreting Results:

The headline value is shown in a convenient unit, while the solve evidence keeps canonical mol/L, mol, g, g/mol, and L values. Changing display precision from 3 to 8 significant figures changes visible rounding only; it does not change the underlying calculation.

• Check the Substance or formula before accepting a formula-derived molar mass.
• Compare As-weighed mass with pure-solute mass whenever purity is below 100%.
• Read final volume as the completed solution volume.
• Do not treat a formula-derived value as appropriate for enriched isotopes, uncertain composition, or a different salt or hydrate.

Technical Details:

IUPAC defines amount concentration as the amount of a constituent divided by the volume of the mixture. Molarity is an older common name for this quantity. The fundamental relationship can be rearranged to solve concentration, amount, or final volume, then combined with molar mass and purity for mass-based paths.

Formula Core:

Let c be molarity, n amount of solute, V final solution volume, M molar mass, m as-weighed mass, and p purity expressed as a decimal fraction.

Lookup Core:

Formula-derived molar mass sums the 2024 CIAAW abridged standard atomic weight for each supported element multiplied by its atom count. A formula may contain element symbols, positive integer subscripts, parentheses, square brackets, and dot-separated hydrate or solvate segments. Capitalization matters.

• Charges, isotope notation, fractional stoichiometry, and spaces are not inferred.
• Positive integer multipliers are limited to 1,000,000, nesting is limited to 10 levels, and total atom counts must remain within the supported range.
• Standard atomic weights describe normal materials and may not fit isotopically enriched or otherwise non-standard samples.

For 5.844 g of 100% NaCl brought to a final volume of 100 mL, the abridged atomic weights give 58.44 g/mol. The amount is 0.1000 mol and the molarity is 1.000 mol/L. Visible digits then follow the selected significant-figure setting.

Accuracy Notes:

• Confirm the chemical entity, hydrate or solvate form, purity basis, and molar-mass source.
• Use final solution volume rather than solvent volume.
• Account for temperature and calibrated glassware when volume accuracy matters.
• Use a manual molar mass approved by the protocol for enriched isotopes or unsupported formula notation.
• Displayed significant figures do not substitute for measurement uncertainty or a laboratory's reporting rules.

Worked Examples:

References:

• Amount Concentration, IUPAC Compendium of Chemical Terminology, 5th edition, 2025.
• Abridged Standard Atomic Weights 2024, Commission on Isotopic Abundances and Atomic Weights.
• Standard Atomic Weights 2024, Commission on Isotopic Abundances and Atomic Weights.