The formula
mass (g) = concentration (mol/L) × volume (L) × molecular weight (g/mol)
Rearrange it to find concentration (mass ÷ volume ÷ MW) or volume (mass ÷ concentration ÷ MW). The calculator handles the unit conversions, so you can enter mM and mL directly.
Worked example
To make 500 mL of 150 mM NaCl (MW 58.44 g/mol): 0.150 mol/L × 0.5 L × 58.44 g/mol = 4.383 g. Dissolve it in less than 500 mL, then make up to the final volume.
Common questions
Which molecular weight should I use for a hydrate?
Use the formula weight of the exact form you are weighing, as printed on the bottle. MgCl₂·6H₂O is 203.30 g/mol, while anhydrous MgCl₂ is 95.21 g/mol, so using the wrong one more than doubles the error.
Is molarity the same as molality?
No. Molarity is moles per litre of solution; molality is moles per kilogram of solvent. Lab recipes almost always mean molarity.
This calculator is checked against independent calculations before every release. How we check our calculators.