Molarity & Mass Calculator — Free Lab Calculators

What this is for: Works out how much solid to weigh to make a solution of a chosen molarity — pick a chemical, set molarity and volume, get the grams.

The formula: mass (g) = molarity (mol/L) × volume (L) × MW (g/mol)

How to use:

Pick your chemical from the dropdown — its formula, MW and CAS number fill in automatically.
Enter the concentration and the volume you want to prepare.
Read off the mass to weigh, in grams and milligrams.
Sections B–D below cover the reverse direction and the % w/v and % v/v helpers.

Solution Calculator — pick a chemical, get the mass to weigh

Pick a chemical from the dropdown — its formula, molecular weight (MW) and CAS number fill in automatically. Then enter the concentration and volume you want to prepare.

Chemical (pick from list)

Target concentration

Target volume

Formula

Molecular weight — MW (g/mol)

CAS number

MASS TO WEIGH OUT (g)

…the same mass in milligrams (mg)

A. Weigh-Out — molarity + volume → grams

Same calculation with the wider unit set (nM, µL) from the workbook's Molarity sheet.

ChemicalMW (g/mol):

Desired concentration

Final volume

GRAMS TO WEIGH (g)

…in milligrams (mg)

B. Reverse — grams + volume → molarity

ChemicalMW (g/mol):

Grams weighed (g)

Final volume

MOLARITY (mol/L)

C. % w/v Helper (% w/v = grams per 100 mL)

Grams of solute (g)

Final volume (mL)

Reverse: desired % w/v

Reverse: final volume (mL)

% w/v

Grams needed for the reverse case (g)

D. % v/v Helper (% v/v = mL solute per 100 mL)

Solute volume (mL)

Final volume (mL)

Reverse: desired % v/v

Reverse: final volume (mL)

% v/v

Solute needed for the reverse case (mL)

Prefer to work offline or keep a copy? The download link is right below.
Download the Molarity & Mass Calculator workbook (.xlsx)

Notes & limits (from the workbook): Mass = MW × concentration × volume. Check the hydrate form on your bottle: the database lists common forms separately (e.g. calcium chloride anhydrous vs dihydrate) and each has its own MW — pick the one you actually have. Entries flagged as liquids in the database (e.g. glacial acetic acid, DMSO) are normally measured by volume, not weighed — the mass shown for them is the equivalent amount, not a bench instruction. A CAS shown as “—” means the database has no CAS number recorded for that entry. Purity is not corrected for: if your chemical is e.g. 98% pure and you need exact molarity, divide the mass by 0.98.