Atom Economy Calculator
A reaction can run at a perfect yield and still waste two thirds of its mass — this is what sees that.
The formula
atom economy = mass of the wanted product / total mass of the reactants, all times their coefficients
A different question from yield
Percent yield asks how much of the possible product you actually recovered. Atom economy asks something the yield cannot see: of all the mass you fed in, how much appears in the product you wanted? A reaction can run at a flawless 100 % yield and still send two thirds of its mass to waste, and nothing in the yield figure would reveal it.
Addition reactions can reach 100 %
If every atom of every reactant ends up in the product, the atom economy is exactly 100 % — ethene plus bromine giving dibromoethane, or nitrogen plus hydrogen giving ammonia. Substitutions and eliminations never can, because they necessarily produce something you did not want. Hydrolysing bromoethane to ethanol is only 31 % economical: the bromine and the sodium leave as salt.
Why it became a design criterion
Barry Trost introduced the measure in 1991 and it reframed how routes are chosen. The Boots synthesis of ibuprofen ran at about 40 % atom economy over six steps; the BHC route that replaced it reaches roughly 77 % in three, and recovers its catalyst besides. The chemistry was not made more efficient in the yield sense — a shorter path was found that wasted fewer atoms.
Balanced first, always
Every quantity on this page depends on a balanced equation. The coefficients set the molar ratio, the ratio sets the theoretical yield, and the yield is what the percentage is measured against. An unbalanced equation does not give a slightly wrong answer — it gives an answer to a different question.