Molarity & Mass Molarity Calculator
Find out how much of a compound to weigh out for a target molar concentration. Enter any three values and leave the one you want to find blank — it solves mass = molarity × volume × molecular weight.
Leave exactly one field blank to solve for it.
How it works
Molar concentration (molarity) is the number of moles of solute per litre of solution, and the number of moles equals mass divided by molecular weight. Putting those together gives mass = molarity × volume × molecular weight.
Enter any three of mass, concentration, volume and molecular weight, and leave the unknown blank — the calculator rearranges the equation and solves it. Mass units (g, mg, µg, ng, kg), concentration units (M, mM, µM, nM) and volume units (L, mL, µL) can be mixed freely; the answer is returned in the unit you selected for the blank field.
Examples
- 1 M NaCl (MW 58.44) in 1 L: mass = 1 M × 1 L × 58.44 g/mol = 58.44 g.
- Make 250 mL of 10 mM Tris (MW 121.14): mass = 0.01 M × 0.25 L × 121.14 = 0.303 g.
- You weighed 0.5 g of a compound (MW 180.16) into 100 mL: concentration = 0.5 / (0.1 × 180.16) = 0.0278 M.
Frequently asked questions
- What is molarity?
- Molarity is the amount of solute in moles per litre of solution, written M (mol/L). A 1 M solution contains one mole of solute in every litre.
- Where do I get the molecular weight?
- It is printed on the reagent bottle, or you can compute it from the chemical formula with a molecular weight calculator.
- Can I mix units?
- Yes. Pick any mass, concentration and volume unit per field; conversions are handled internally and the result is shown in the unit you chose for the blank field.
- How is this different from a dilution calculator?
- A dilution calculator (C1V1 = C2V2) works out how to dilute an existing stock solution. This calculator works out how much solid compound to weigh out to make a solution from scratch.