Molarity Calculator
Calculate the molarity of a solution - or find moles or volume from the other values.
📖 What is Molarity?
Molarity is the most widely used measure of solution concentration in chemistry. It is defined as the number of moles of solute (the substance being dissolved) per litre of solution. Represented by the symbol M or mol/L, molarity tells you how "concentrated" a solution is.
A 1 M solution of sodium chloride (NaCl) contains 1 mole of NaCl - that's 58.44 grams - dissolved in enough water to make exactly 1 litre of solution. A 0.1 M solution contains one-tenth as much.
Molarity is the standard unit used in preparing reagents, performing titrations, calculating reaction stoichiometry, and analysing chemical equilibria. Understanding how to calculate and use molarity is fundamental to all quantitative chemistry, from school laboratory work to pharmaceutical manufacturing and industrial chemical production.
The relationship between molarity, moles, and volume is simple: M = n/V. From this one formula, you can find any of the three values if the other two are known - which is exactly what this calculator does.
📐 Formula
Molarity (M) = Moles of Solute / Volume of Solution (in litres)
M = n / V
Moles (n) = M × V
Volume (V) = n / M
Moles from mass: n = mass (g) / Molecular Weight (g/mol)
📖 How to Use This Calculator
1
Select what you want to find: Molarity, Moles, or Volume.
2
Enter the two known values.
3
Optionally, use the mass → moles converter if you know the mass and molecular weight instead of moles directly.
4
Click Calculate.
💡 Example Calculations
Example 1 - Finding molarity
1
You dissolve 5.85 g of NaCl (MW = 58.5 g/mol) in water to make 200 mL (0.2 L) of solution.
2
Moles = 5.85 / 58.5 = 0.1 mol
3
Molarity = 0.1 / 0.2 = 0.5 M
Example 2 - Finding volume needed
1
You need to prepare 250 mL of a 0.1 M HCl solution from a stock 2 M HCl solution.
2
Using C1V1 = C2V2: V1 = (0.1 × 0.250) / 2 = 0.0125 L = 12.5 mL
3
Take 12.5 mL of the 2 M stock and dilute to 250 mL with water.
Frequently Asked Questions
What is molarity?
Molarity (M) is a measure of the concentration of a solution, defined as the number of moles of solute dissolved per litre of solution. A 1 M (1 molar) solution contains 1 mole of solute in 1 litre of solution. It is the most common unit of concentration in chemistry.
What is the difference between molarity and molality?
Molarity (M) = moles of solute / litres of solution. Molality (m) = moles of solute / kilograms of solvent. Molarity is volume-based and changes with temperature (since volume changes). Molality is mass-based and temperature-independent, preferred for properties like boiling point elevation.
How do I calculate moles from grams?
Moles = Mass (grams) / Molecular Weight (g/mol). For example, to find moles in 18 g of water (H₂O, MW = 18 g/mol): moles = 18 / 18 = 1 mole. Use the Molecular Weight Calculator to find MW from a chemical formula.
What is the dilution formula?
When you dilute a solution by adding more solvent, the number of moles of solute stays constant: C1V1 = C2V2. If you have 100 mL of a 2 M solution and dilute to 400 mL, the new concentration is: C2 = (2 × 100) / 400 = 0.5 M.
What is a standard solution?
A standard solution is a solution of precisely known concentration, used as a reference in titrations and analytical chemistry. To make 500 mL of a 0.1 M NaCl solution: moles needed = 0.1 × 0.5 = 0.05 mol; mass NaCl = 0.05 × 58.44 = 2.922 g - dissolve this in water and make up to 500 mL.
How do you prepare a 1M solution?
To prepare 1 litre of a 1 molar (1M) solution: (1) Calculate the molar mass of the solute (from the periodic table). (2) Weigh out that number of grams. (3) Dissolve in a small amount of distilled water. (4) Transfer to a 1 litre volumetric flask. (5) Add distilled water up to the 1 litre mark. Example: to make 1L of 1M NaCl: molar mass of NaCl = 23 + 35.5 = 58.5 g/mol. Weigh 58.5 g of NaCl, dissolve, and make up to 1 litre.
What is the difference between a solute and a solvent?
A solute is the substance dissolved in a solution - present in a smaller amount. A solvent is the substance that dissolves the solute - present in the larger amount. In a saline solution (NaCl in water), NaCl is the solute and water is the solvent. Molarity expresses the amount of solute relative to the total volume of solution. When preparing solutions in the lab, you dissolve the solute in part of the solvent, then bring the total volume up to the target using a volumetric flask.
How do I prepare a solution of a specific molarity from a stock solution?
Use the dilution formula: C1V1 = C2V2, where C1 is the stock concentration, V1 is the volume of stock needed, C2 is the desired final concentration, and V2 is the final volume. Example: to prepare 100 mL of 0.1 M HCl from a 12 M stock, calculate V1 = (0.1 x 100) / 12 = 0.83 mL. Add 0.83 mL of concentrated HCl to approximately 90 mL of water in a volumetric flask, then top up to exactly 100 mL. Always add acid to water, never water to acid, for safety.
How do I prepare a 1 M solution of NaCl?
Molar mass of NaCl = 23 + 35.45 = 58.45 g/mol. To make 1 L of 1 M NaCl: dissolve 58.45 g of NaCl in a small volume of distilled water, transfer to a 1 L volumetric flask, and add water to the 1 L mark. Never add the full 1 L first - volumetric glassware is designed for final volume, not initial volume. For 500 mL, use 29.23 g.
What is the difference between molarity and normality?
Molarity (M) counts moles of solute per litre of solution. Normality (N) counts equivalents per litre, where equivalents depend on the reaction type. For acids, 1 equivalent = 1 mole of H+ ions. For HCl (monoprotic), N = M. For H2SO4 (diprotic), N = 2M. Normality is used in acid-base and redox titrations for direct stoichiometric comparison, but modern chemistry increasingly uses molarity for all purposes.