Molarity Calculator

What this calculator does

The Molarity Calculator relates the amount of solute, its molar mass, the volume of solution, and the concentration. It can solve for any one of those four quantities when the other three are known. The result panel also reports the concentration in several forms, including molarity in moles per liter, mass concentration in grams per liter, and the number of moles of solute.

Molarity is one of the most common ways to express concentration. A 1 molar solution contains 1 mole of solute per liter of solution. It is used to prepare laboratory solutions, calculate reaction stoichiometry, and describe biological and pharmaceutical concentrations.

How to use this calculator

1. Choose what you want to solve for: molarity, mass, molar mass, or volume.
2. Enter the other three values.
3. Select the units for mass, molar mass, volume, and concentration.
4. Click Calculate.

The default example dissolves 100 grams of sodium chloride (58.44 g/mol) in enough water to make 2 liters of solution. The molarity is about 0.8556 mol/L, the mass concentration is 50 g/L, and the solution contains about 1.7112 moles of solute.

Formulas

The basic definition of molarity is:

M = n ÷ V

M is molarity in moles per liter, n is moles of solute, and V is the volume of solution in liters. When mass is known instead of moles:

n = m ÷ MW
M = m ÷ (MW × V)

Here m is the solute mass in grams and MW is the molar mass in grams per mole. Rearranging the equation gives the other solve modes:

m = M × MW × V
MW = m ÷ (n × V)
V = n ÷ M

What the results mean

The headline shows the value you asked for. The summary rows show molarity, mass concentration, moles of solute, mass of solute, molar mass, solution volume, and concentration in the selected unit.

Mass concentration is solute mass divided by solution volume, reported in grams per liter. Dividing grams per liter by grams per mole produces moles per liter.

When a mass-based concentration unit such as g/L, mg/L, ppm, or ppb is selected, the calculator converts it to a mass concentration and then uses the molar mass to obtain molarity. Parts per million and per billion are treated as milligrams per liter and micrograms per liter, assuming a dilute aqueous solution with a density near 1 kg/L.

Assumptions and limitations

• Volume means the final solution volume, not the solvent volume added. Dissolving a solute can change the total volume.
• Full dissolution is assumed; dissociation, ionic strength, activity coefficients, and precipitation are not modeled.
• Molarity changes slightly with temperature because solution volume changes; molality, based on solvent mass, does not.
• For ppm and ppb, the dilute aqueous assumption described above applies.
• The calculator does not handle multiple solutes or reactions between solutes.
• Zero mass, volume, or concentration is rejected where it would appear in a denominator.
• Displayed values are rounded. Use calibrated equipment and validated methods for analytical work.

Frequently asked questions

What is the difference between molarity and molality?

Molarity is moles of solute per liter of solution. Molality is moles of solute per kilogram of solvent. Molarity depends on solution volume, which can change with temperature; molality depends on solvent mass, which does not.

How do I find molarity from mass and volume?

Divide the solute mass by its molar mass to get moles, then divide by the solution volume in liters. For example, 10 grams of NaCl (58.44 g/mol) in 0.5 liters gives 10 ÷ 58.44 ÷ 0.5 = 0.342 mol/L.

Can I use this calculator for a concentration in g/L?

Yes. Select a mass concentration unit, enter the value, and provide the molar mass. The calculator converts grams per liter to molarity by dividing by the molar mass.

Source

Reference: Calculator.net — Molarity Calculator. Molar mass values and SI definitions can be checked against IUPAC and NIST references.

Disclaimer

This calculator is intended for education and routine laboratory planning. It is not a substitute for validated analytical methods, safety procedures, or professional chemical judgment.