Molar Mass Calculator
Grams per mole for any formula from IUPAC atomic weights.
What it does
Molar mass converts between weighable grams and countable moles by adding atomic weights across the formula. Water totals two hydrogens plus one oxygen; every other compound follows the same addition with its own counts.
The tool above takes a plain formula with element symbols and counts. It returns grams per mole with the per element breakdown beside it.
The default H2O reads 2.016 + 15.999 = 18.015 g/mol. Table salt NaCl reads 22.99 + 35.45 = 58.44, matching the molarity page example, while glucose totals 180.156.
Atomic weights follow IUPAC standard values with NIST atomic weight references behind them. Both revise values as measurements improve, so tables carry the current year.
How to use
- Type the formula with capitals right: H2O, not h2o.
- Add counts after symbols, omitting 1.
- Read grams per mole first for weighing.
- Use the breakdown to check each element share.
- Feed the result into the molarity page for solutions.
Formula
- atomic weight
- IUPAC grams per mole of each element.
- count
- Subscript atoms of that element.
- sum
- Total across all element groups.
Twenty nine common elements are built in; exotic ones report unknown instead of guessing. Parentheses need expanding first (Ca(OH)2 becomes CaO2H2).
Worked example
Example: H2O
Formula H2O.
- Hydrogen: 2 x 1.008 = 2.016.
- Oxygen: 1 x 15.999 = 15.999.
- Total: 2.016 + 15.999 = 18.015 g/mol.
- Check: one liter of water weighs about 1000 g, near 55.5 mol.
- Tool shows 18.015 g/mol with the split.
Reference table
| Formula | Molar mass | Use |
|---|---|---|
| H2O | 18.015 g/mol | Water baseline |
| CO2 | 44.009 g/mol | Gas work |
| NaCl | 58.44 g/mol | 1 M solutions |
| C6H12O6 | 180.156 g/mol | Glucose |
| CaCO3 | 100.086 g/mol | Limestone |
Limits
- 29 common elements only.
- No brackets, hydrates, or charges parsed.
- Isotopes use standard averages, not enriched values.
- Naming help absent; symbols must be right.
Common mistakes
- Lowercasing symbols (CO vs Co differ).
- Reading Cl as C plus I.
- Forgetting unwritten counts mean one.
- Using outdated rounded weights for precise work.
- Entering hydrates like CuSO4.5H2O raw.
Try it yourself
Quick checks. Answers sit tucked under each question.
CO2?
12.011 + 2 x 15.999 = 44.009 g/mol.
NaCl?
22.99 + 35.45 = 58.44 g/mol.
O2?
2 x 15.999 = 31.998 g/mol.
Questions
What is molar mass of water?
18.015 g/mol: two hydrogens plus one oxygen.
Molar mass vs molecular weight?
Same number; mass per mole in g/mol versus relative units.
Why capitals matter?
CO is carbon monoxide while Co is cobalt: case changes elements.
How do brackets work here?
Expand first: Ca(OH)2 enters as CaO2H2.
Which weights are used?
IUPAC standard atomic weights, the current published values.
Moles from grams?
Divide grams by this result; the molarity page continues the path.