What this calculator solves

Calculate the solute mass required from molarity or mass concentration and a final solution volume. Molar presets run only when the exact chemical form and molecular weight are reviewed.

Scientific review date: 2026-09-16

Formula and variables

mass (g) = molarity (mol/L) × final volume (L) × molecular weight (g/mol)

  • • Molarity is moles per litre of final solution.
  • • Final volume means the completed solution volume, not the starting solvent volume.
  • • Molecular weight must match the actual salt or hydrate form.

Worked example

Example: 500 mL of 5 M NaCl

Use anhydrous NaCl at 58.44 g/mol, a target of 5 M, and a final volume of 0.5 L.

5 × 0.5 × 58.44 = 146.10 g NaCl

Supported modes

molaritymass concentration

Scientifically reviewed presets

5 M NaCl solution (500 mL)

500 mL — Sodium chloride (anhydrous): 5 M

Why results may differ

  • • Reagent purity is not corrected automatically.
  • • A different salt or hydrate form requires a different molecular weight.
  • • Bring the solution to 500 mL final volume; do not add the solute to 500 mL of solvent.

Common questions

How many grams are needed for 500 mL of a 1 M solution?

The answer depends on molecular weight: 500 mL at 1 M contains 0.5 mol, so use 0.5 × molecular weight in grams.

Does a hydrate form change the answer?

Yes. An anhydrous compound and its hydrate have different molecular weights, so confirm the exact bottle form.