molarity calculator

What is molarity?

Molarity is one of the most common concentration units in chemistry. It tells you how many moles of solute are present in one liter of total solution. The symbol for molarity is M, and the unit is mol/L.

If you are preparing lab solutions, analyzing titration data, or working chemistry homework, molarity is often the first concentration tool you need.

Molarity formula (and related equations)

The core equation is:

• M = n / V

Where:

• M = molarity (mol/L)
• n = moles of solute (mol)
• V = volume of solution (L)

From that one equation, you can rearrange to solve for moles or volume:

• n = M × V
• V = n / M

For dilution problems, use:

• M1V1 = M2V2

How to use this molarity calculator

1) Calculate molarity from moles and volume

Choose Molarity (M = n / V), enter moles and total solution volume, then calculate.

2) Calculate moles from molarity and volume

Choose Moles (n = M × V). This is useful when you know concentration and want to find how many moles are present in a flask, beaker, or aliquot.

3) Calculate required volume

Choose Volume (V = n / M) if you know the amount of substance and desired concentration.

4) Convert mass to molarity

If you know mass in grams, enter molar mass to convert grams to moles first. The calculator then computes concentration using total volume.

5) Solve dilution setups

In Dilution mode, the calculator tells you how much stock solution to pipette and how much solvent to add to reach the final concentration and volume.

Quick unit reminders

• 1000 mL = 1 L
• 1 L = 0.001 m³
• Always convert volume to liters before applying M = n/V

Most concentration mistakes happen when mL is used directly in the formula without converting to liters.

Worked examples

Example 1: Molarity from moles

You dissolve 0.25 mol NaCl and make the total solution volume 0.50 L:

• M = 0.25 / 0.50 = 0.50 M

Example 2: Moles from concentration

You have 200 mL of 1.2 M HCl:

• Convert 200 mL to 0.200 L
• n = 1.2 × 0.200 = 0.24 mol

Example 3: Dilution

Prepare 250 mL of 0.10 M solution from a 1.0 M stock:

• V1 = (M2 × V2) / M1 = (0.10 × 250 mL) / 1.0 = 25 mL
• Measure 25 mL stock, then add solvent to 250 mL total.

Common mistakes to avoid

• Using solvent volume instead of final solution volume
• Skipping mL-to-L conversion
• Using wrong molar mass (check hydration state and formula)
• Rounding too early in multi-step calculations

Molarity vs other concentration units

Molarity (M)

Moles of solute per liter of solution. Easy for most aqueous lab work.

Molality (m)

Moles of solute per kilogram of solvent. Better when temperature changes matter significantly.

Mass percent

Mass of solute divided by total mass of solution, multiplied by 100.

Final notes

This calculator is designed for fast, practical chemistry calculations used in classrooms and labs. For best results, keep units consistent, verify significant figures, and cross-check unusual outputs with dimensional analysis.