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Molarity Calculator (Mass, Molecular Weight, Volume, Concentration)

Fill in any three values and get the fourth: how much to weigh, how much solution you can make, what concentration you end up with, or the molecular weight. Units switch between mg and g, mL and L, and μM, mM and M.

Inputs

Solve for

g/mol

Results

Mass
14.61

Formula

Mass (g) = Conc. (mol/L) × Volume (L) × MW (g/mol)

Conc. (mol/L) = Mass ÷ (Volume × MW)

Volume (L) = Mass ÷ (Conc. × MW)

Tip: Units convert automatically: 1 M = 1000 mM = 10⁶ μM, 1 L = 1000 mL, 1 g = 1000 mg. For hydrates, use the MW that includes the water.

You got this step right, but a whole experiment has dozens of linked parameters. Change one dilution factor and everything downstream has to be recalculated. In Vara the parameters of your whole experiment are connected, so changing one recalculates the rest automatically. Manage 3 experiments for free.

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FAQ

How many grams of NaCl do I need for 500 mL of 0.5 M?+
NaCl has a molecular weight of 58.44 g/mol. Mass = concentration × volume × molecular weight = 0.5 mol/L × 0.5 L × 58.44 g/mol = 14.61 g. Dissolve 14.61 g of NaCl in about 400 mL of water, then bring it up to 500 mL.
How do M, mM and μM convert?+
1 M = 1 mol/L = 1000 mM = 1,000,000 μM, so 100 mM is 0.1 M. Pick the unit in the calculator and it converts for you; there is no need to convert to M first.
Where do I find the molecular weight, and what about hydrates?+
Use the MW or FW on the bottle label or datasheet. For a hydrate, use the molecular weight that includes the water: CaCl₂·2H₂O is 147.01 g/mol while anhydrous CaCl₂ is 110.98 g/mol. Mixing them up throws your weighing off by about 25%.
I already weighed the powder. How do I get the concentration?+
Set Solve for to concentration and enter the mass, molecular weight and final volume. For example, 14.61 g of NaCl made up to 500 mL gives 14.61 ÷ (0.5 × 58.44) = 0.5 M, or 500 mM.
Why bring it up to volume instead of just adding 500 mL of water?+
The dissolved solute takes up space too. Add 500 mL of water and the final volume ends up above 500 mL, so the concentration comes out low. Dissolve in less water than you need, then top up to the mark.

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