Elemental Analysis Calculator
Calculate the molecular weight and mass percent composition of a compound.
Select up to four elements with their atom counts to get results.
Elemental analysis tells you what percentage of a compound’s mass comes from each element. Every compound has a fixed mass composition determined entirely by its chemical formula.
Molar mass = Σ (number of atoms × atomic mass of that element)
Mass percent of element X = (atoms_X × M_X) / molar mass × 100
For water (H₂O): M = 2×1.008 + 1×15.999 = 18.015 g/mol %H = 2×1.008 / 18.015 × 100 = 11.19% %O = 15.999 / 18.015 × 100 = 88.81%
For glucose (C₆H₁₂O₆): M = 6×12.011 + 12×1.008 + 6×15.999 = 180.156 g/mol %C = 72.066/180.156 = 40.00%, %H = 12.096/180.156 = 6.71%, %O = 95.994/180.156 = 53.29%
The percentages always sum to 100% — use this as a sanity check.
Elemental analysis is how chemists verify a newly synthesized compound is what they think it is. A combustion analyzer burns the compound and measures the CO₂ and H₂O produced to determine %C and %H; %N comes from a separate measurement. If the measured percentages match the theoretical values for the proposed formula, the synthesis was likely successful.
The inverse problem — given the mass percentages, find the empirical formula — is also a classic chemistry calculation. Divide each percentage by the element’s atomic mass to get the mole ratios, then reduce to the smallest integers.
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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