Molar Mass Calculator
| Formula | Name | Molar mass (g/mol) |
|---|---|---|
| H2O | water | 18.015 |
| CO2 | carbon dioxide | 44.009 |
| NaCl | table salt | 58.440 |
| C6H12O6 | glucose | 180.156 |
| CH4 | methane | 16.043 |
| NH3 | ammonia | 17.031 |
| H2SO4 | sulfuric acid | 98.072 |
| CaCO3 | calcium carbonate | 100.086 |
| O2 | oxygen gas | 31.998 |
| N2 | nitrogen gas | 28.014 |
Molar mass is the exchange rate between a chemical recipe and the lab scale: grams per mole, read straight off the formula. This calculator parses formulas - including parentheses like Ca(OH)2 - using the standard atomic weights from NIST, and the reference table of ten common compounds is computed from the same weights at build time.
The parser covers the 21 most common elements; anything rarer (or a typo) comes back as a named error instead of a wrong number, which is the honest failure mode for homework and lab prep alike.
How to use
- Type a formula - subscripts as plain digits, parentheses for groups; the chips load water, lime and glucose.
- Copy puts the exact g/mol value on the clipboard for a lab worksheet.
- Check the reference table for the ten compounds every general-chemistry problem set reuses.
Frequently asked questions
Why is chlorine 35.45 and not a whole number?
Atomic weights on the table are weighted averages over natural isotope mixes: chlorine is about 75% Chlorine-35 and 25% Chlorine-37, landing at 35.45. Only synthetic and single-isotope elements get near-whole numbers - the average is what balances equations and grams in real labs.
How do I compute molar mass of a hydrate like CuSO4·5H2O?
Add the parts: copper sulfate plus five waters - 159.6 plus 5 × 18.015 = 249.7 g/mol. The dot means add, not multiply; this calculator handles each half separately (paste CuSO4, then 5H2O as 5 waters of H2O) if the dot syntax is not accepted.
What exactly is a mole?
Exactly 6.02214076×10²³ particles - a definition fixed by the 2019 SI redefinition, same event that made the speed of light exact. Molar mass in g/mol is numerically the mass of that many formula units: one mole of water molecules weighs 18.015 grams.
Why does my textbook say 98.08 for sulfuric acid but the calculator says 98.072?
Rounding depth on sulfur: NIST lists S as 32.06, older tables used 32.065 or 32.064 - a difference of about 0.008 g/mol. The calculator reports what its NIST weights sum to, which is the reproducible answer; quote your source’s precision in the lab writeup.