Quick start
- Choose Find M: moles when you know moles and final solution volume.
- Choose Find M: grams when you know grams, molar mass, and final solution volume.
- Choose Find moles when you know molarity and final solution volume.
- Choose Find grams when you know molarity, final solution volume, and molar mass.
- Select liters or milliliters to match the volume in your question.
Best uses
Use this guide to turn a classroom or lab-planning question into the correct formula and calculator mode.
- Calculate molarity from moles and liters.
- Calculate molarity from grams, molar mass, and final volume.
- Calculate moles from molarity and final volume.
- Calculate grams from molarity, final volume, and molar mass.
What this calculator is solving
The Molarity Calculator solves four common chemistry setups: molarity from moles, molarity from grams, moles from molarity, and grams from molarity.
Match each input label on the calculator to the value you need to find, molarity in mol/L, moles or grams of solute, molar mass in g/mol when needed, and final solution volume in L or mL.
The formula in plain language
In plain language: The calculator uses M = n / V, n = M x V, grams = M x V x molar mass, or M = grams / (molar mass x V). M is molarity, n is moles, and V is final solution volume in liters. The examples on the page are there so you can compare your inputs with a worked example before copying the answer.
Use M = n / V for molarity, n = M x V for moles, grams = M x V x molar mass, or M = grams / (molar mass x V). M means mol/L, n means moles, and V means liters of final solution.
How to read the answer
Read the unit with the main answer. M means mol/L, mol means moles of solute, and g means grams of solute. The result card also shows the liters used after any mL conversion.
- A molarity result uses M, which means moles of solute per liter of final solution.
- A moles result uses mol and tells you the chemical amount needed for the entered concentration and volume.
- A grams result uses g and includes the moles and molar mass used in the conversion.
- Final volume shows the entered mL value and its liter conversion when you select milliliters.
Common mistakes to avoid
The answer changes when you use milliliters as though they were liters, enter solvent volume instead of final solution volume, or use the molar mass for the wrong compound or hydrate.
- Use 0.5 L for 500 mL. A missing division by 1,000 makes the answer 1,000 times too large or too small.
- Use final solution volume after the solute dissolves and the solution reaches its mark.
- Convert grams and moles with the molar mass for the exact compound and hydration state.
- Keep full calculator precision through the intermediate moles step, then round the final answer to the required significant figures.
- Check solute purity, safety procedures, and lab instructions before using the number in real lab work.
The four molarity formulas
Find molarity from moles with M = n / V. Find moles from molarity with n = M x V. In both formulas, V must be the final solution volume in liters.
When the problem uses mass, connect grams and moles with molar mass. Use grams = M x V x molar mass, or M = grams / (molar mass x V).
Example: calculate moles from molarity and volume
Suppose a question asks how many moles are in 500 mL of a 0.2 M solution. Convert 500 mL to 0.5 L, then use n = M x V.
The calculation is 0.2 mol/L x 0.5 L = 0.1 mol. Choose Find moles, enter 0.2 M and 500 mL, and check that the result card also shows 0.5 L.
Example: calculate grams from molarity
For 500 mL of 0.2 M NaCl, the moles step gives 0.1 mol. Using a NaCl molar mass of 58.44 g/mol, multiply 0.1 mol x 58.44 g/mol = 5.844 g.
Choose Find grams and enter 0.2 M, 500 mL, and 58.44 g/mol. The calculator keeps the moles step unrounded before it calculates grams.
Example: calculate molarity from grams
Start with 5.844 g NaCl, a molar mass of 58.44 g/mol, and 500 mL final solution volume. Divide 5.844 g by 58.44 g/mol to get 0.1 mol.
Convert 500 mL to 0.5 L, then divide 0.1 mol by 0.5 L. The result is 0.2 M.
Final solution volume and molar mass checks
Molarity uses the final volume of the whole solution. In a volumetric flask, that often means dissolving the solute and then filling to the final mark.
Molar mass must match the exact formula. An anhydrous compound and its hydrate can have different g/mol values. Use the Molecular Weight Calculator as a classroom check, then confirm the value required by your source or procedure.
What the calculator cannot approve
The calculator checks arithmetic and units. Your teacher, lab manual, or procedure sets the required compound, purity, significant figures, equipment, and safety steps.
For real lab work, check the safety data sheet, hydration state, measurement uncertainty, temperature requirements, and whether the procedure prepares a solution to final volume.
Research and references
These references help check the measurements, units, limits, or safety notes used in this guide.
Worked examples for Molarity Calculator
0.2 M after converting 500 mL to 0.5 L
0.2 M
0.1 mol after converting 500 mL to 0.5 L
5.844 g NaCl
FAQ in plain language
What does M mean in the Molarity Calculator?
M means molarity in moles per liter. A 0.2 M answer means the final solution contains 0.2 mol of solute per liter of solution.
Which molarity mode should I choose?
Choose the mode named for the missing value. The four choices find molarity from moles, molarity from grams, moles from molarity, or grams from molarity.
How do I calculate moles from molarity and volume?
Multiply molarity by final solution volume in liters. For 0.2 M and 500 mL, convert 500 mL to 0.5 L, then calculate 0.2 x 0.5 = 0.1 mol.
How do I calculate grams from molarity?
Multiply molarity by final volume in liters and molar mass. For 0.2 M NaCl, 500 mL, and 58.44 g/mol, calculate 0.2 x 0.5 x 58.44 = 5.844 g.
How do I calculate molarity from grams?
Divide grams by molar mass to get moles, then divide moles by final solution volume in liters. For 5.844 g NaCl in 500 mL, the result is 0.2 M.
Can I enter milliliters instead of liters?
Yes. Select milliliters and the calculator converts the volume to liters before using the formula. It shows both values in the result card.
Why does final solution volume matter?
Molarity uses the volume after the solute dissolves and the solution reaches its final mark. The starting solvent volume may differ from the final solution volume.
Related tools
- Molecular Weight CalculatorCalculate molar mass from a chemical formula with element counts, parentheses, hydrates, and mass shares.
- Conversion CalculatorConvert length, mass, volume, and temperature units with clear formula steps.
- Density CalculatorCalculate density from mass and volume with a custom unit label.
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