Molar Mass Calculator
Type a chemical formula and get its molar mass, with a breakdown of what it is made of.
Results
Molar mass
249.6770
g/mol
What it is made of
Cu 1 63.5460 25.45 %
S 1 32.0600 12.84 %
O 9 143.9910 57.67 %
H 10 10.0800 4.04 %
Every atom added up
CuSO9H10
Grams to weigh out
249.6770
g
Moles in what you have
0.040052
mol
Atoms in one molecule
21
Elements
4
Element that weighs most of it
O
Uses a mass number, not a standard weight
No
Which elements those are
—
What this tool does
Write the formula the way you would on paper. Brackets multiply what is inside them, so Ca(OH)₂ counts two oxygens and two hydrogens. Water of crystallisation goes after a dot — CuSO4.5H2O, CuSO4*5H2O and CuSO4·5H2O all work and all count the five waters. The atomic weights are the conventional abridged values published by IUPAC. That matters more than it sounds: sulfur is 32.06 in the current table and 32.065 in older ones, which is why you will see sulfuric acid quoted as both 98.07 and 98.08. Neither is wrong; what would be wrong is mixing the two tables in one calculation, and this never does.
Formula
molar mass = sum of (atomic weight × how many atoms)
Variables
| Symbol | Meaning | Unit |
|---|---|---|
formula | Chemical formula | — |
moles | Moles you want to weigh out | mol |
grams | Grams you have on the scale | g |
MM | Molar mass | g/mol |
TB | What it is made of | — |
FC | Every atom added up | — |
GM | Grams to weigh out | g |
MG | Moles in what you have | mol |
AT | Atoms in one molecule | — |
EL | Elements | — |
HV | Element that weighs most of it | — |
ES | Uses a mass number, not a standard weight | — |
EW | Which elements those are | — |
Worked example
- Chemical formulaCuSO4.5H2O
- Moles you want to weigh out1 mol
- Grams you have on the scale10 g
- Molar mass249.6770 g/mol
- What it is made ofCu 1 63.5460 25.45 % S 1 32.0600 12.84 % O 9 143.9910 57.67 % H 10 10.0800 4.04 %
- Every atom added upCuSO9H10
- Grams to weigh out249.6770 g
- Moles in what you have0.040052 mol
- Atoms in one molecule21
- Elements4
- Element that weighs most of itO
- Uses a mass number, not a standard weightNo
- Which elements those are—
Limitations
- For work that must comply with a standard or be signed off, check the result against the applicable code and have it reviewed by a qualified engineer.
- The calculation runs at full precision and only the display is rounded. If you copy an intermediate value and retype it, small differences can appear.