Molarity Calculator
Amount concentration
Enter your values, then calculate to see a verified result.
BMI Range (Adults)
FormulaVersioned calculationv2.5.0
What is calculated
Molarity and, when mass is entered, mass concentration from the exact solute amount and final solution volume.
Supported inputs
- Mass
- g, mg or kg
- Amount
- mol, mmol or µmol
- Volume
- L, mL or µL
Important limitation
The denominator is final solution volume. The result does not determine safety, solubility, pH, activity, or reaction yield.
Normalize inputsConvert the entered units to mol, g, and L
500.0 mL = 0.5000 LFind molesUse entered moles or divide mass by molar mass
n = m / MrDivide by volumeUse completed solution volume
c = n / VInterpretation
The amount concentration is .
Moles are calculated from the entered amount before division by final volume.
Displayed decimals do not establish laboratory measurement accuracy.
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Public verification recordFormula v2.5.0
- Review scope
- Formula, Units, Labels, Validation, Content Package, And Internal-route Implementation
- Review team
- CalculatorGeek Algorithmic Team
- Verified
- Next source review
- Automated fixtures
- 6 cases
Review method
Formula identities, unit normalization, supplied acceptance cases, invalid boundaries, links, and rendered output are checked separately.
Known limitations
- Final solution volume, not starting solvent volume, is the denominator.
- Molar mass must match the exact chemical form used.
- Purity, solubility, pH, activity, reaction yield, and chemical safety are outside this calculation.
Primary sources
- IUPAC Gold Book: amount concentration
- BIPM: SI base unit mole
- PubChem: sodium chloride
- NIST Guide for the Use of the International System of Units
Latest update
2026-09-09 · Rebuilt only the Molarity calculator and approved cluster from the dedicated package.
Published calculation checks
| Case | Inputs | Expected result |
|---|---|---|
| Main sodium chloride reference | {"basis":{"value":"mass"},"mass":{"value":5,"unit":"g"},"molar_mass":{"value":58.44,"unit":"g/mol"},"volume":{"value":500,"unit":"mL"}} | {"molarity":0.1711156742,"mass_concentration":10} |
| Mass and volume unit equivalence | {"basis":{"value":"mass"},"mass":{"value":500,"unit":"mg"},"molar_mass":{"value":58.44,"unit":"g/mol"},"volume":{"value":50,"unit":"mL"}} | {"molarity":0.1711156742,"mass_concentration":10} |
| Known moles reference | {"basis":{"value":"moles"},"moles_input":{"value":0.5,"unit":"mol"},"volume":{"value":2,"unit":"L"}} | {"molarity":0.25} |
On this page
Molarity formula
Molarity, more formally called amount concentration, is the amount of a constituent divided by the volume of the mixture. In common laboratory units:
c = n / V
where:
cis molarity in moles per liter, mol/L;nis amount of solute in moles, mol;Vis final solution volume in liters, L.
When solute mass and molar mass are known:
n = m / M_r
Therefore:
c = m / (M_r × V)
Here m is solute mass in grams and M_r is the entered molar mass in grams per mole. The interface may use “molecular weight,” but molar mass is the dimensioned quantity used in the calculation.
Continue with the How to Calculate Molarity. check the equation and unit sequence.
How to use the calculator
- Enter the mass of the solute and select its unit.
- Enter the molar mass for the exact chemical form used, including waters of hydration where applicable.
- Enter the final volume of the completed solution and select its unit.
- Calculate the result.
- Check the normalized grams, liters, and formula substitution before using the displayed value.
Do not enter the volume of solvent added at the beginning unless it is also the measured final solution volume. Dissolving a solute can change the total volume.
Continue with the How to Prepare a Molar Solution. translate a target concentration into required mass.
Worked example using sodium chloride
Suppose 5.00 g of sodium chloride is brought to a final solution volume of 500.0 mL. PubChem lists a molecular weight of 58.44 g/mol for sodium chloride.
Convert the final volume:
500.0 mL = 0.5000 L
Calculate moles:
n = 5.00 g / 58.44 g/mol = 0.08556 mol
Calculate molarity:
c = 0.08556 mol / 0.5000 L = 0.1711 mol/L
With the significant figures supported by these inputs, report the result as approximately 0.171 M.
The corresponding mass concentration is:
5.00 g / 0.5000 L = 10.0 g/L
Molarity and mass concentration are different outputs. Molarity uses amount of substance per volume; mass concentration uses mass per volume.
How the calculator should process inputs
The implementation should normalize each input before calculation:
- mass to grams;
- molar mass to grams per mole;
- final solution volume to liters.
It should retain adequate internal precision, calculate moles, calculate molarity, and round only the displayed result. If the page offers M, mM, micromolar, or nanomolar output, convert from the unrounded base result.
The secondary output currently labelled “Concentration” should be labelled Mass concentration. Its help text should state that it is solute mass divided by final solution volume. Remove the existing comparison with density.
Molarity units
| Unit | Equivalent in mol/L | Symbol |
|---|---|---|
| molar | 1 | M |
| millimolar | 10^-3 | mM |
| micromolar | 10^-6 | µM |
| nanomolar | 10^-9 | nM |
| picomolar | 10^-12 | pM |
For example, 0.00250 M = 2.50 mM = 2,500 µM.
Assumptions and limitations
- The denominator is final solution volume, not solvent volume.
- The molar mass must match the material used. An anhydrous compound and a hydrate have different molar masses.
- Purity or assay is not applied unless the calculator has a separate, verified purity input.
- The result is an analytical amount concentration for the entered chemical entity. It does not automatically calculate the concentrations of ions after dissociation.
- Molarity is volume-based and can change when temperature changes solution volume.
- Displayed decimals do not prove measurement accuracy. The balance, glassware, reagent, and inputs determine practical uncertainty.
- The calculator does not determine solubility, reaction yield, pH, chemical activity, compatibility, or safe handling.
Common mistakes
- Entering milliliters as liters without converting.
- Using starting water volume instead of final solution volume.
- Using the molar mass of the wrong hydrate, salt, or reagent form.
- Confusing molarity with molality, mass percent, normality, or mass concentration.
- Rounding moles before the final division.
- Treating
0.1 Mand0.1 mMas equivalent; they differ by a factor of 1,000.
Frequently asked questions
How do I calculate molarity from grams?
Divide solute mass in grams by molar mass in grams per mole to obtain moles. Divide those moles by final solution volume in liters. In one expression, c = m / (M_r × V).
Is molarity based on solution volume or solvent volume?
Molarity is based on the final volume of the solution. Adding solute to a measured volume of solvent does not necessarily leave the total volume unchanged.
What is the difference between M and mM?
1 M = 1,000 mM. A value of 0.025 M is therefore 25 mM.
Can molarity be negative?
A physical amount concentration is not negative. The interface should reject negative mass, molar mass, or volume values.
Does temperature affect molarity?
Molarity can change with temperature because it is defined using solution volume. Molality uses solvent mass and is not affected by thermal expansion in the same way.
Can this calculator prepare a safe laboratory solution?
It performs concentration arithmetic only. It does not evaluate hazards, incompatibilities, exothermic mixing, solubility, purity, equipment, or laboratory procedure. Follow the reagent's safety data and an approved protocol.