It reads real formulas
Brackets nest to any depth, so Ca(OH)2, Al2(SO4)3 and K3[Fe(CN)6] all parse correctly. Hydrates work with a dot, an asterisk or a full stop — CuSO4·5H2O, CuSO4*5H2O and CuSO4.5H2O are the same thing, and the multiplier applies to everything after the dot.
Two-letter symbols always win over two one-letter ones, so Co is cobalt rather than carbon plus oxygen. Capitalisation matters for the same reason: CO is carbon monoxide, Co is not.
Percent composition
The bar and the table show what fraction of the mass each element contributes. This is what a chemist means by composition, and it is often more useful than the total: it tells you how much of a fertiliser is actually nitrogen, or how much of an ore is actually iron.
Water is a good example of why it is not obvious. Two thirds of the atoms are hydrogen, but hydrogen is only 11% of the mass — because oxygen is sixteen times heavier.
Moles are just a counting unit
A mole is 6.022 × 10²³ of something, chosen so that one mole of a substance weighs its molar mass in grams. That is the whole trick: it lets you weigh out an exact number of molecules on an ordinary balance.
Type into either box below and the other follows. The particle counts are shown too — both formula units and total atoms, which are different numbers and easy to confuse.
Frequently asked questions
Why is my answer slightly different from my textbook's?
Different sources round atomic masses differently. These are the IUPAC 2021 conventional values; a table using 12.01 for carbon instead of 12.011 will drift by a few hundredths on a large molecule.
What does the calculator do with an unknown element?
It refuses rather than guessing, and names the symbol it could not recognise. A silent wrong answer is worse than an error message.
Is anything uploaded?
No. The formula you enter is parsed in the page and not stored.
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