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Molarity Calculator

This calculator solves M=m/(MW×V)M=m/(MW\times V) for molarity, mass, volume, or molecular weight (MW) from the other three. Calculate For toggles the unknown; Common Compounds presets (NaCl, HCl, NaOH, glucose) fill MW. Units include M, mM, g/L, ppm, g, mL, L, and more. Decimal places 2–6 (default 4). Ideal solution only; not molality or dilution.

By Jeff Beem

Updated

Settings

Calculate For

Common Compounds

Select a compound to auto-fill molecular weight, or enter manually below.

Molecular Weight (MW)

Mass of Solute

Volume of Solution

Results

Enter the known values to calculate

How to use this calculator

Set Decimal places, pick Calculate For, then fill molecular weight (MW) and the three known fields. Common Compounds can auto-fill MW for NaCl, HCl, NaOH, or glucose. The dark Results card shows the solved value; Unit conversions list related concentration, mass, or volume units. The Information hub below explains the core formula and how molarity differs from molality.

Information hub

The core formula

M = molarity (mol/L), m = mass of solute (g), MW = molecular weight (g/mol), V = volume of solution (L).

Mass (g)÷(MW × V)=Molarity

Common units

  • M = mol/L
  • mM = mmol/L
  • µM = µmol/L

Volume in L; mass in g; MW in g/mol.

Molarity vs molality: don’t mix them up

Molarity is moles of solute per liter of solution. It depends on the total volume of the mixture (solute + solvent). When you add more solute or change temperature, the volume can change, so molarity can change.

Molality is moles of solute per kilogram of solvent only. It ignores the volume of the solute. Molality is temperature-independent and preferred for colligative properties (boiling-point elevation, freezing-point depression).

M=nVsolutionM = \frac{n}{V_{\text{solution}}}vsm=nmsolventm = \frac{n}{m_{\text{solvent}}}

This calculator uses molarity. For dilute aqueous solutions near room temperature, molarity and molality are often close, but they are not the same.

Reading your molarity result

The dark Results card shows the solved variable in your chosen unit. Unit conversions appear below when applicable. Match decimal places in Settings before copying numbers.

Example: 5.844 g NaCl in 1 L → 0.1000 M

Calculate For → Molarity. Select NaCl, mass 5.844 g, volume 1 L, MW 58.44 g/mol. Primary result 0.1 M; conversions list mM, μM, nM, and mol/m³ at your decimal setting.

Example: Mass for 0.5 M in 250 mL

Calculate For → Mass. Concentration 0.5 M, NaCl MW 58.44, volume 250 mL → mass about 7.305 g. Weigh that amount and dilute to the mark for a 0.5 M stock.

Molarity calculator

Solve M = m/(MW × V) for concentration, mass, volume, or molecular weight. Fields start empty until you enter values; runs locally.

What this calculator does

Rearranges M=mMW×VM=\frac{m}{MW\times V} for any one unknown: molarity (mol/L), solute mass, solution volume, or molecular weight (MW). Accepts mixed units (grams, milliliters (mL), mM, g/L, ppm, and others) with internal conversion to g, L, and mol/L. Four compound presets auto-fill MW; molality and dilution math are out of scope.
  • Limits:
    Ideal-solution model; no activity coefficients, temperature correction, or solvent-only volume. Mass concentration via ppm assumes dilute aqueous ≈ mg/L.

How the math works

Convert inputs to base units, apply the rearranged formula for the selected mode, then convert the result back to your display unit.
M=mMW×VM=\frac{m}{MW\times V}
Check (molarity mode): 11.69 g NaCl, MW 58.44, volume 500 mL → M=11.6958.44×0.5≈0.4001M=\frac{11.69}{58.44\times 0.5}\approx 0.4001 M at four decimals.

Limits

Does not compute molality, normality, or serial dilution volumes. Compound list is four entries, not a full reagent database. Educational reference; verify lab preparations independently.

Molarity Calculator FAQ

Which unit conversions appear for molarity results?

When solving for molarity, the Results card lists M, mM, μM, nM, and mol/m³ at your decimal setting. Mass and volume modes show their own conversion rows (g, mg, L, mL, and others).

What does each Calculate For mode need?

Molarity: mass, MW, volume. Mass: concentration, MW, volume. Volume: concentration, mass, MW. Molecular Weight: concentration, mass, volume. The field you are solving for hides; fill the other three. Non-positive inputs are ignored.

Which concentration units work besides molar (M)?

Molar units: M, mM, μM, nM, mol/m³. Mass-based: g/L, mg/L, parts per million (ppm), parts per billion (ppb), kg/L, kg/m³, g/m³. For g/L and ppm the tool converts through MW to mol/L internally; enter MW for the solute.

How many compounds are in Common Compounds?

Four presets: NaCl (58.44), HCl (36.46), NaOH (40.0), C₆H₁₂O₆ glucose (180.16) g/mol. Selecting one fills MW; you can still edit the field or type any MW manually.

What do decimal places control?

Settings → Decimal places (default 4, options 2–6) rounds the primary result and the Unit conversions list. Very large or tiny values may show scientific notation.

How is molarity different from molality?

Molarity is moles per liter of solution; molality is moles per kilogram of solvent. This page computes molarity only. The Information hub contrasts the two for colligative-property work where molality is preferred.

Why not add solid to exactly 1 L of water for a 1 M stock?

Dissolved solute increases total volume. For 1 M NaCl you want 58.44 g dissolved and diluted to a 1 L volumetric mark, not 58.44 g dropped into 1 L of water (final volume exceeds 1 L, concentration ends below 1 M).

How is this different from the molecular weight calculator?

This page solves M=m/(MW×V)M=m/(MW\times V) for concentration, mass, volume, or MW when you know the other three. The molecular weight calculator parses a chemical formula to find MW; copy that value here if needed.

Sources & citations

References used for the calculation method and definitions. Links open in a new tab when available.

[1]
IUPAC — Quantities, Units and Symbols in Physical Chemistry (Gold Book)

IUPAC definition of amount-of-substance concentration (molarity).

Science & Lab Reference Note

Educational Use: These tools use standard scientific formulas and accepted constants. Results are intended for learning, homework, and general reference, not for regulated lab work, industrial processes, or clinical applications.

Verification Recommended: Real-world conditions (purity, temperature, pressure, humidity) affect outcomes. For research, manufacturing, or safety-critical work, confirm with a qualified professional or calibrated lab equipment.

Not Professional Advice: This site does not provide chemical, medical, or engineering advice. All calculations run locally in your browser; no data is stored or transmitted.

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