How this calculator works
Divide each element mass by its IUPAC 2021 atomic weight. Normalize to the smallest molar amount and search multipliers up to 24 for a small whole-number ratio within 0.015. Mass percentages describe a hypothetical 100 g sample. Ambiguous rounded data should be checked against analytical uncertainty rather than treated as proof of a unique formula.
Formula
n_i = m_i/A_i; ratio_i = n_i/min(n). Molecular multiplier = measured molar mass / empirical formula mass.
Worked example
12.011 g C, 2.016 g H and 15.999 g O give amounts 1:2:1 and CH2O. A molecular molar mass of 180.156 g/mol gives C6H12O6.
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Frequently asked questions
How many elements can I enter?
One to ten distinct symbols, with the same number of positive masses or percentages.
Do masses need to total 100?
No. Only percentage input must total 100 within the stated tolerance.
Why can rounded data fail?
Limited precision can obscure integer ratios. Improve the measurements rather than forcing an arbitrary formula.