Molarity Calculator
Calculate concentration from mass and volume
Molarity is the amount of solute, in moles, divided by the final solution volume, in liters. When you know a mass instead of a number of moles, first divide that mass by the molar mass. In symbols, c = n / V = m / (Mₘ × V), where c is concentration in mol/L, n is amount in mol, m is mass in g, Mₘ is molar mass in g/mol, and V is solution volume in L.
For example, enter 1000 mg of solute, a molar mass of 100 g/mol, and a final solution volume of 100 mL. The mass is 1 g and the volume is 0.1 L. Dividing 1 g by 100 g/mol gives 0.01 mol; dividing that by 0.1 L gives 0.1 mol/L, or 0.1 M.
Find solute mass or solution volume
Choose the quantity you want in the Calculate menu. To find mass, the tool uses m = c × V × Mₘ. A concentration of 0.1 M in 100 mL, with a molar mass of 100 g/mol, corresponds to 1 g of solute. To find volume, it uses V = m / (Mₘ × c): 1 g with the same molar mass at 0.1 M corresponds to 0.1 L of solution.
The selected unknown is removed from the input fields, so it cannot conflict with your known values. Each mode shows the amount of solute and the calculation steps. Results use the unrounded intermediate numbers; the displayed steps use up to eight significant digits for readability.
Keep the units visible
A milligram is 0.001 g, and a milliliter is 0.001 L. For the example above, treating 100 mL as 100 L would give 0.0001 M instead of 0.1 M: a result 1,000 times too small. The conversion lines make this scale change visible before the formula is applied.
Changing an input unit converts the value already entered. Molar mass always uses g/mol. Concentration results include M, mM, µM, and nM; mass results include grams and metric equivalents; volume results include liters, milliliters, and microliters. Very small or large results use scientific notation.
What the arithmetic assumes
The inputs must refer to the same solute and solution. Use the mass of the solute itself and an appropriate molar mass, rather than the mass of a mixture or an unidentified material. The final solution volume is required; the calculator does not infer it from solvent volume, density, or mixing separate liquids.
This tool evaluates the concentration equation. It does not check solubility, purity, chemical compatibility, temperature effects on volume, or whether a proposed solution can be made. It provides no experimental procedure or dosing instructions. Dilution from a stock solution and acid/base normality are separate calculations.
Blank or invalid required fields clear the answer. Clear values removes the example inputs. Calculations run in your browser; tool analytics do not include the masses, volumes, concentrations, or results you enter or calculate.
Frequently asked questions
How do I calculate molarity from grams?
Divide the solute mass in grams by its molar mass in g/mol to get moles. Then divide those moles by the final solution volume in liters. The calculator converts your selected mass and volume units before applying this formula.
What is the difference between M and mM?
M means mol/L. One M equals 1,000 mM, 1,000,000 µM, or 1,000,000,000 nM. A concentration of 0.1 M is therefore 100 mM. Uppercase M is used here for molarity; lowercase m is often used for molality, a different quantity.
Can this calculator find mass or volume instead?
Yes. Choose Solute mass or Final solution volume in the Calculate menu. Enter the other two quantities and the solute's molar mass in g/mol. The result includes the rearranged formula and unit conversions.
Should I enter solution volume or solvent volume?
Enter the final volume of the whole solution. The volume of solvent added is not automatically the final solution volume, and separately measured component volumes should not simply be added and treated as a verified final volume.
Is molar mass the same as molecular weight?
Many calculators label a g/mol field as molecular weight. This tool calls it molar mass because g/mol is mass per mole. Enter a molar mass appropriate to the substance you mean, including its hydrate form when applicable. The tool does not identify a substance or calculate its molar mass from a chemical formula.
Is molarity the same as molality?
No. Molarity divides moles of solute by liters of solution. Molality divides moles of solute by kilograms of solvent. This calculator finds molarity and does not convert molality, mass percent, or ppm into molarity.