Molarity Calculator
Work out how much to weigh for a solution of a given concentration, or the concentration or volume from what you weighed.
Calculator
Make a solution
From the bottle's label. Hydrates weigh more than the dry salt.
Enter the formula weight, concentration and final volume to see the mass to weigh.
Worked example
500 mL of 150 mM sodium chloride
- 01c = 150 mM = 0.150 mol/L, V = 500 mL = 0.500 L, MW = 58.44 g/mol
- 02m = 0.150 × 0.500 × 58.44
- 03m = 4.383 g
Weigh 4.383 g of NaCl, dissolve it, and make up to 500 mL.
How it works
The reasoning behind it
Molarity is the number of moles of a substance in one litre of solution. A mole of anything weighs its formula weight in grams, so one mole of NaCl weighs 58.44 g.
To make a solution you need c × V moles, and those moles weigh c × V × MW grams. The same equation, rearranged, gives the concentration from a mass you weighed (c = m ÷ (MW × V)) or the volume to make it up to (V = m ÷ (MW × c)).
The units have to agree: grams, litres and mol/L. The calculator converts mg, µL or mM before it multiplies.
Questions
Frequently asked
How do I calculate molarity from grams?
Divide the mass in grams by the formula weight to get moles, then divide by the volume of solution in litres. 2.922 g of NaCl (58.44 g/mol) in 100 mL is 0.05 mol ÷ 0.1 L = 0.5 M.
How do I convert mg/mL to molarity?
mg/mL is the same as g/L. Divide it by the formula weight in g/mol to get mol/L. 5 mg/mL of glucose (180.16 g/mol) is 5 ÷ 180.16 = 0.0278 M, or 27.8 mM.
What is the difference between molarity and molality?
Molarity is moles per litre of solution; molality is moles per kilogram of solvent. Molality doesn't change with temperature, so physical chemistry uses it. In the lab, solutions are made up by volume, so molarity is the one you need.
Is formula weight the same as molecular weight?
For this calculation, yes: both mean the mass of one mole in grams. Formula weight is the stricter term for salts such as NaCl, which are not made of separate molecules. Use the value on the bottle, because it includes any water of hydration.
More Calculators
Each one shows its formula and a worked example, so you can check the answer and learn the method.
Dilution Calculator
How much stock to dilute, or the final concentration or volume, with C₁V₁ = C₂V₂.
Open calculatormg/dL to mmol/L Converter
Convert glucose, cholesterol, creatinine, HbA1c and other results between conventional and SI units.
Open calculatorHenderson–Hasselbalch Calculator
The pH of a buffer, or how much of its acid and base form you need for a target pH, with common buffers built in.
Open calculator