Molarity Calculator

You choose how you're starting, from a mass of solute or from moles, then enter the values and the solution volume. From a mass it finds the moles by dividing by the molar mass, then divides those moles by the volume in liters for the molarity. Everything loads instantly in the page, so you'll see the concentration update as you type, and your numbers never leave your device. It also shows the moles and the grams-per-liter alongside.

Molarity is moles of solute divided by liters of solution. If you have a mass, first turn it into moles by dividing the grams by the molar mass, then divide by the volume. So 58.44 grams of table salt, which has a molar mass of 58.44, is exactly 1 mole, and dissolved in 1 liter that's a molarity of 1, written 1 M. The calculator runs both steps the moment you type the mass, molar mass, and volume.

Molarity is the most common way to express concentration in chemistry: the number of moles of a dissolved substance per liter of solution. A 2 M solution has 2 moles in every liter. It's written with a capital M, so 0.5 M reads as half-molar. Because reactions happen mole for mole, molarity lets you measure out exact amounts for a reaction, which is why it shows up all over lab work and homework.

They sound alike but divide by different things. Molarity is moles per liter of solution, while molality is moles per kilogram of solvent. Molarity is easier to measure, since you just make up a volume, so it's the everyday choice. Molality matters when temperature changes, because volume shifts with heat but mass doesn't, so it's used for boiling-point and freezing-point work. This tool calculates molarity, the one you'll meet most often.

Add up the atomic masses of every atom in the formula. For table salt, NaCl, sodium is about 22.99 and chlorine about 35.45, so the molar mass is 58.44 grams per mole. For water, two hydrogens at 1.008 plus one oxygen at 16.00 gives 18.02. Once you have that number, type it into the molar mass box here, or let the molar mass calculator add it up from the formula for you. The reference table below lists a few common compounds too.

When a concentration is given in grams per liter, divide it by the molar mass to get the molarity in moles per liter. Take 58.44 grams per liter of table salt: dividing by the molar mass of 58.44 lands on 1 M. The step works because grams per liter over grams per mole cancels to moles per liter, which is molarity by definition. If the concentration already sits in a molar unit, no real conversion is needed, so 500 mM is just 0.5 M.

Multiply the molarity by the molar mass to reach grams per liter, then by the volume in liters for the total grams. A 0.25 M glucose solution, molar mass 180.16, carries 0.25 times 180.16, or about 45 grams in every liter. Make up 2 liters of it and you'll weigh out 0.25 times 180.16 times 2, close to 90 grams. Molarity to grams is really the concentration calculation run in reverse.

Yes, it's completely free, with no sign-up, and it runs right in your browser, so nothing you type is uploaded. Pick your starting point, type the mass or moles and the volume, and read the molarity in a tap. Bookmark it for chemistry class, lab prep, or making up solutions, and you'll have the molarity formula, the moles, and the concentration all in one place whenever you need them.