Solution Concentration Calculator
Concentration tells you how much solute sits in a given amount of solution, and it can be expressed several ways. This calculator takes the solute mass in grams, the molar mass in grams per mole, the solution volume in milliliters, and the solution density, then reports moles of solute, molarity in mol/L, mass per volume in g/L, and mass percent. Every figure follows the standard IUPAC definitions, so the result is exact for the inputs you provide. Use NIST atomic weights to look up the molar mass of your compound.
Concentration formula
Moles = solute mass / molar mass
Volume in liters = volume mL / 1000
Molarity = moles / volume in liters
Mass per volume = solute mass / volume in liters
Solution mass = volume mL * density
Mass percent = solute mass / solution mass * 100
These are the standard IUPAC definitions of amount of substance and concentration. No empirical constant is assumed; the only physical input is the solution density, which you set.
Concentration units explained
- Molarity (mol/L, symbol M) is the most common lab concentration unit for reactions in solution.
- Moles of solute come from mass divided by molar mass, the atomic-weight sum from the NIST tables.
- Mass per volume (g/L) is handy for buffers and biological media specified by weight.
- Mass percent compares solute mass to total solution mass, common in industrial mixtures.
- Pure water has a density near 1 g/mL at room temperature, so 1 mL is roughly 1 g.
Solution concentration: frequently asked questions
What is molarity?
Molarity is the number of moles of solute per liter of solution, with the unit mol/L (M). It is defined as moles of solute divided by volume of solution in liters. Moles of solute equals the solute mass in grams divided by the molar mass in grams per mole.
How do I find the molar mass to enter?
Molar mass is the sum of the atomic masses of every atom in the formula, in grams per mole. The IUPAC and NIST atomic weights tables list each element. For example sodium chloride (NaCl) is about 22.99 plus 35.45, which equals 58.44 g/mol.
What is the difference between molarity and mass percent?
Molarity uses moles per liter of solution. Mass percent is the mass of solute divided by the total mass of solution, multiplied by 100. This calculator reports both, plus mass per volume in grams per liter, so you can pick the unit your protocol requires.
Does this assume the solution density equals water?
For mass percent the calculator needs total solution mass. It uses the solution mass you can derive from volume and density. The default treats 1 mL as 1 g (the density of water at room temperature). For non-aqueous or concentrated solutions, adjust the volume or compute mass percent from your measured solution mass.
Why is the number very small for dilute solutions?
Dilute solutions have low molarity, sometimes well below 0.01 mol/L. The calculator switches to scientific notation for values that would otherwise round to 0.00, so a genuinely tiny concentration is shown accurately rather than as zero.
Official sources
- National Institute of Standards and Technology: Atomic Weights and Isotopic Compositions.
- NIST: Avogadro constant and the mole definition.
Reviewed by the CalculatorHub team, edited by James Graham, 16 June 2026. See our methodology.