Mass calculator
Find out how much compound you need to weigh out. Enter the molecular weight, the desired volume and molar concentration, and the required mass is calculated for you.
How the calculation works
Multiply the target concentration by the volume to get the amount of substance you need, then multiply by the molecular weight to turn moles into grams: m = C × V × MW. Enter concentration in mM, volume in mL and MW in g/mol; the calculator returns the mass in mg. No unit juggling.
Worked example
A 1 mL stock at 10 mM of a compound with MW 250 g/mol takes 0.01 × 1 × 250 = 2.5 mg of solid. Scaling up changes nothing in the method: for 50 mL of a 2 mM working solution of a compound with MW 180.2 g/mol, you weigh out 18 mg.
Related tools
Already weighed the compound and want to know what molarity you ended up with? Use the concentration calculator. Working from a fixed mass toward a target molarity? The volume calculator tells you how much solvent to add. Every compound we stock lists its molecular weight on its catalog page.
Frequently asked questions
The calculated mass is too small to weigh. What now?
Weigh out at least 1-2 mg and scale the solvent volume up by the same factor. Below a milligram, balance error dominates the result.
Should I correct for purity?
For exact work, yes. Divide the calculated mass by the purity fraction: a compound at 95% purity needs the mass divided by 0.95.
My compound is a salt or hydrate. Which MW goes in?
The MW of the actual solid, counting the counterion and any water of crystallization. That's what sits on the balance.
Why are 10 mM DMSO stocks so common?
Most screening compounds stay dissolved in DMSO at 10 mM, and the dilution math down to assay concentrations stays simple. It's been the default in compound management for years.