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.