Enter mass % of elements to find the simplest whole-number ratio.
The empirical formula shows the simplest whole-number ratio of atoms in a compound. Steps: (1) Convert percent composition to grams (assume 100 g sample). (2) Divide each element's mass by its atomic weight to get moles. (3) Divide all mole values by the smallest. (4) Round to nearest whole numbers — if you get x.5, multiply all by 2; if x.33, multiply by 3. Example: 40.0% C, 6.7% H, 53.3% O → moles: 3.33, 6.65, 3.33 → ratio 1:2:1 → empirical formula CH₂O (formaldehyde). To get the molecular formula, divide the actual molar mass by the empirical formula mass: n = M/EFM, then multiply subscripts by n. For glucose: 180/30 = 6, so molecular formula = C₆H₁₂O₆.