100 g of glucose, C6H12O6
Molar mass is 6×12.01 + 12×1.008 + 6×16.00 = 180.16 g/mol, so 100 g is 100 / 180.16 ≈ 0.5551 mol.
Molar mass & stoichiometry calculator
Result
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How it works
The formula is read symbol by symbol: a capital letter starts an element symbol, an optional lowercase letter continues it, and any digits that follow give its count in the formula. Parentheses group a sub-unit that a following number multiplies as a whole — Fe2(SO4)3 means 2 iron atoms plus three lots of (one sulfur, four oxygen), for 3 sulfur and 12 oxygen in total.
Molar mass is the sum of each element’s standard atomic weight multiplied by how many times it appears. It is numerically the same value as molecular weight (in unified atomic mass units) but expressed per mole, in grams per mole — which is what actually gets weighed on a balance.
Moles link a countable number of particles (via Avogadro’s number) to a mass you can measure. Given a molar mass M, a mass m corresponds to n = m / M moles, and n moles corresponds to a mass of n × M.
Formulas used
Molar mass
M = Σ (atomic weight × count)
Moles from mass
n = m / M
- n
- Amount of substance, in moles
- m
- Mass, in grams
- M
- Molar mass, in g/mol
Worked examples
0.5 mol of iron(III) sulfate, Fe2(SO4)3
Molar mass is 2×55.85 + 3×32.07 + 12×16.00 = 399.91 g/mol, so 0.5 mol weighs about 199.96 g.
Assumptions and limits
- Atomic weights are the IUPAC 2021 standard values for naturally occurring element mixtures, not a specific isotope.
- The formula is read literally — it does not check that the resulting compound is chemically real or balanced.
Frequently asked questions
How do I write hydrates, like copper sulfate pentahydrate?
Write the two parts and let the tool add their molar masses separately if needed — for CuSO4·5H2O, computing CuSO4 (159.6 g/mol) and 5×H2O (90.08 g/mol) and adding them gives 249.7 g/mol. The middle dot notation itself is not parsed automatically.
Why does the formula need exact capitalisation?
Element symbols are case-sensitive by convention: Co is cobalt, but CO would be carbon monoxide (carbon + oxygen). Getting the case right is what lets a two-letter symbol like Na, Cl or Fe be told apart from two separate one-letter elements.
Updated