Molarity (M) is the concentration of a solute in solution, measured in moles per litre. Formula: M = n ÷ V, where n is moles of solute and V is volume of solution in litres. A 0.5 M NaCl solution contains 0.5 moles (29.22 g) of NaCl per litre of solution. Used everywhere in chemistry, biology and biochemistry — buffers, reagents, antibody stocks, antibiotic dilutions all get expressed in molarity.

How do I make a 0.5 M NaCl solution?

To make 100 mL of 0.5 M NaCl: weigh out 2.92 g of NaCl (mass = molarity × volume × molar mass = 0.5 × 0.100 × 58.44). Dissolve in about 80 mL of deionised water, then top up to a final volume of exactly 100 mL in a volumetric flask. Don't dissolve in 100 mL of water — solute takes up space, so the final volume would be slightly more than 100 mL.

How do I convert between M, mM, µM and nM?

Each unit step is a factor of 1,000. 1 M = 1,000 mM = 1,000,000 µM = 1,000,000,000 nM. So 100 mM = 0.1 M = 100,000 µM. To convert down (M to mM): multiply by 1,000. To convert up (µM to mM): divide by 1,000. Biology labs typically use mM for buffers (50 mM Tris, 150 mM NaCl), µM for enzyme reactions and small-molecule inhibitors, nM and pM for antibodies and high-affinity ligands.

What's the difference between molarity, molality and normality?

Molarity (M) is mol solute per litre of solution. Molality (m) is mol solute per kg of solvent. Normality (N) is equivalents per litre — depends on the reaction context. Molarity is by far the most common in modern chemistry and biology. Molality is used when temperature changes matter (because mass doesn't change with temperature but volume does). Normality is mostly used in acid-base titrations and is being phased out of teaching.

How do I work out moles from mass and molar mass?

moles = mass ÷ molar mass. So 5.844 g of NaCl (molar mass 58.44 g/mol) = 5.844 ÷ 58.44 = 0.1 mol. For mixed compounds, calculate molar mass by summing atomic masses from the periodic table (NaCl = 22.99 + 35.45 = 58.44 g/mol). The calculator above will accept mass and molar mass directly so you don't need a separate moles calculator.

Molarity Calculator

Editorially reviewed Reviewed by Agarapu Ramesh, science educator (chemistry). LinkedIn

Last reviewed: May 2026 | Standard chemistry formulas and IUPAC conventions

Solve M = moles / liters for molarity, moles, or solution volume.

What can you solve?

Enter two values and leave exactly one blank. The calculator rearranges the same relationship, converts mL to L when needed, and draws a solution-volume view so the concentration setup is easier to inspect.

Unknown	Known values	Rearranged formula
Molarity M	moles and volume	M = n / V
Moles n	molarity and volume	n = M x V
Volume V	moles and molarity	V = n / M
mL volume	choose mL unit	mL / 1000 = L before solving

Formula used

M = n / V, where n = moles of solute and V = final solution volume in liters.

Worked examples

Find molarity: 0.500 mol NaCl in 1.00 L gives M = 0.500 / 1.00 = 0.500 M.

Find moles: 250 mL of 0.50 M solution is 0.250 L, so n = 0.50 x 0.250 = 0.125 mol.

Find volume: to make 0.200 M from 0.100 mol, V = 0.100 / 0.200 = 0.500 L, or 500 mL.

Why solution volume matters

Molarity is based on final solution volume, not just the water poured into a beaker. In a volumetric flask, the usual workflow is to dissolve the solute first, then add solvent until the final mark is reached. That is why the diagram emphasizes the solution level and not only the amount of solute.

Where molarity is useful

Preparing standard solutions from known moles of solute.
Finding moles available in titration and reaction calculations.
Checking dilution problems before using M1V1 = M2V2.
Converting between molar concentration and stoichiometry amounts.
Reviewing unit conversions between mL, L, mol, and M.

Common mistakes

Using mL directly in the denominator instead of liters.
Entering grams where the formula requires moles.
Using solvent volume instead of final solution volume.
Leaving two blanks, which makes the problem underdetermined.
Assuming molarity stays unchanged after evaporation or temperature-driven volume change.

Rounding and result checking

Report molarity in mol/L or M. A quick estimate catches many mistakes: if 0.5 mol is dissolved in 2 L, the answer must be less than 0.5 M; if the same moles are placed in a smaller final volume, the molarity must increase. Keep extra digits while calculating, then round the final answer to the limiting measured value.

Related Chemistry Tools

Molar Mass Calculator Mole Gram Particles Converter Dilution Calculator Molality and Normality Calculator Limiting Reagent Calculator Henderson-Hasselbalch Calculator

Molar Calculator

A molar calculator usually means a molarity check: M = moles of solute ÷ litres of solution. If you know grams instead of moles, divide grams by molar mass first, then divide by volume in litres.

FAQs

What is molarity?

Molarity (M) is the most common way of expressing solution concentration in chemistry: it is the number of moles of solute per litre of solution. Definition: M = moles of solute ÷ volume of solution in litres, with units mol/L (often written 'M'). Note 'volume of solution', not 'volume of solvent' — when you make 1 L of 1 M NaOH, you dissolve 40.00 g of NaOH and dilute to a final volume of 1.000 L using a volumetric flask. Worked example: dissolving 4.00 g of NaOH (= 0.100 mol) and making the final volume 500 mL gives M = 0.100 mol ÷ 0.500 L = 0.200 mol/L. Molarity is the standard form for titrations and dilutions because volumes are quick to measure with a buret or volumetric flask.

How to calculate concentration molarity?

Use M = moles of solute ÷ volume of solution in litres. If the problem gives a mass, first convert to moles with moles = mass ÷ molar mass. If the volume is in mL, divide by 1000 to get litres. Example 1: 5.85 g of NaCl (M_NaCl = 58.44 g/mol) in 250 mL of solution → 5.85 ÷ 58.44 = 0.100 mol; 0.100 ÷ 0.250 = 0.400 M. Example 2: 0.050 mol of HCl in 200 mL → 0.050 ÷ 0.200 = 0.25 M. Always use the volume of the final solution, not the volume of solvent added; the small expansion or contraction on dissolution is automatically captured when you make up to the mark in a volumetric flask.

How to find pH from molarity?

It depends on whether the solute is an acid or base, and whether it is strong or weak. Strong monoprotic acid (HCl, HNO3): [H+] = molarity, so pH = -log(M). 0.01 M HCl → pH = 2.00. Strong polyprotic acid: account for stoichiometry (H2SO4 first dissociation is essentially complete: 0.01 M H2SO4 → ~0.02 M H+ → pH ≈ 1.70). Strong base (NaOH, KOH): pOH = -log(M), pH = 14.00 - pOH. 0.001 M NaOH → pOH = 3.00, pH = 11.00. Weak acid: solve the Ka equilibrium. For a dilute, monoprotic weak acid the simple approximation is [H+] ≈ √(Ka × C), so pH ≈ -log(√(Ka × C)). Weak base: [OH-] ≈ √(Kb × C); convert via pOH = -log[OH-], pH = 14 - pOH.

Is molarity the same as concentration?

Molarity is one form of concentration, not a synonym. Concentration is the general idea of how much solute is present per amount of solvent or solution. Common forms: Molarity (M) — mol of solute per L of solution. Molality (m) — mol of solute per kg of solvent (used in colligative-property calculations because it doesn't depend on temperature). Mass percent (% w/w) — g solute per 100 g solution. Volume percent (% v/v) — for liquid-in-liquid mixtures. Normality (N) — equivalents of solute per L of solution (used in acid-base and redox titrations). Mole fraction (X) — mol of one component ÷ total mol of all components. ppm and ppb — for very dilute solutions. Always read units carefully: '0.1 M' is a molarity; '10% NaCl' is a mass percent; '5 ppm fluoride' is parts per million.

How to convert percent mass into molarity given density?

Use M = (10 × % mass × density) ÷ molar mass, where density is in g/mL and molar mass in g/mol. Derivation: take 1.000 L = 1000 mL of solution; its mass is 1000 × density (g); the solute mass is (% / 100) × that; divide by the solute's molar mass to get moles; the result is per 1 L, which is the molarity. Worked example for concentrated HCl (37% by mass, density 1.18 g/mL, molar mass 36.46 g/mol): M = (10 × 37 × 1.18) ÷ 36.46 = 436.6 ÷ 36.46 ≈ 11.97 mol/L, usually rounded to 12 M. The same formula gives concentrated H2SO4 (98%, 1.84 g/mL, 98.08 g/mol) → 18.4 M; concentrated HNO3 (70%, 1.42 g/mL, 63.01 g/mol) → 15.8 M.

How to find moles from molarity?

Rearrange the molarity definition: moles = molarity × volume (in litres). Make sure to convert millilitres to litres (divide by 1000) before multiplying. Examples: 250 mL of 0.5 M NaOH → 0.5 × 0.250 = 0.125 mol; 2.0 L of 3.0 M HCl → 3.0 × 2.0 = 6.0 mol. From moles you can get mass with mass = moles × molar mass. So 0.125 mol of NaOH is 0.125 × 40.00 = 5.00 g. This conversion is the bridge from a solution measurement (volume + concentration) to a stoichiometric quantity (moles), which is what every titration and reaction calculation ultimately needs.

How to find molarity of NaOH?

Two common cases. Case 1 — solid NaOH dissolved in known volume: M = (mass / 40.00) ÷ V (in L). Example: 8.00 g NaOH in 500 mL → 0.200 mol ÷ 0.500 L = 0.400 M. Case 2 — titration against a standard acid using the 1:1 stoichiometry of NaOH + HCl → NaCl + H2O. With M1 V1 = M2 V2: 25.0 mL of NaOH neutralizes 30.0 mL of 0.100 M HCl → M(NaOH) = (0.100 × 30.0) ÷ 25.0 = 0.120 M. Practical note: NaOH is hygroscopic and slowly absorbs CO2 from the air to form Na2CO3. Solid NaOH masses are therefore unreliable for high-accuracy work; for analytical use, prepare the solution at the approximate concentration and standardize it by titration against a primary standard such as potassium hydrogen phthalate (KHP) or oxalic acid dihydrate.

How to calculate molarity in titration?

Use the stoichiometric form of the dilution-style equation: n1 M1 V1 = n2 M2 V2, where n is the stoichiometric coefficient of each species in the balanced equation. For 1:1 reactions (NaOH + HCl → NaCl + H2O) the n's cancel, leaving the simpler M1 V1 = M2 V2. Procedure: balance the reaction, record volumes at the endpoint, plug in the known molarity and volume, solve for the unknown molarity. Example: 20.0 mL of NaOH neutralizes 25.0 mL of 0.100 M H2SO4 in 2 NaOH + H2SO4 → Na2SO4 + 2 H2O. With n(NaOH) = 2 and n(H2SO4) = 1: 2 × M(NaOH) × 20.0 = 1 × 0.100 × 25.0 → M(NaOH) = 2.5 / 40.0 = 0.0625 M. Choose an indicator whose pH transition matches the equivalence-point pH: phenolphthalein (transition near pH 8-10) for strong acid + strong base or weak acid + strong base; methyl orange (3-4) for strong acid + weak base.