Atom Economy Calculator

Last updated: June 2026

Use this atom economy calculator to determine the percentage of reactant mass that can theoretically become the desired product. It is designed for O-Level, IGCSE, A-Level and Singapore H2 Chemistry students studying green chemistry and reaction efficiency.

Key takeaway: Atom economy compares the mass contribution of the desired product with the total mass contribution of all reactants in the balanced equation. A higher value means that less reactant mass is converted into unwanted by-products.
How to use this atom economy calculator
  1. Write or check the balanced chemical equation.
  2. Enter the coefficient and Mr of the desired product.
  3. Enter the coefficient and Mr of every reactant.
  4. Leave unused optional reactant rows blank.
  5. Press Calculate to see the mass contributions, atom economy and theoretical waste percentage.

What is atom economy?

Atom economy measures how efficiently a chemical reaction incorporates atoms from its reactants into a desired product. Atoms that do not enter the desired product appear in by-products and contribute to waste.

Atom economy formula

atom economy = coefficient × Mr of desired product / total coefficient × Mr of reactants × 100%

Coefficients from the balanced equation must be included. Only the desired product belongs in the numerator.

How to calculate atom economy

First calculate the mass contribution of the desired product by multiplying its coefficient by its Mr. Then calculate the mass contribution of each reactant in the same way and add these reactant contributions together.

Finally, divide the desired-product contribution by the total reactant contribution and multiply by 100%.

Atom economy versus percentage yield

Atom economy is determined from the balanced equation and measures the theoretical use of atoms. Percentage yield compares the actual amount of product obtained with the theoretical amount.

A reaction may have high atom economy but low percentage yield, or high percentage yield but poor atom economy.

Worked examples

Addition of hydrogen to ethene

C2H4 + H2 → C2H6

The reactant mass contribution is 28.0 + 2.0 = 30.0, while the desired product contributes 30.0. The atom economy is therefore 100%.

Thermal decomposition of calcium carbonate

CaCO3 → CaO + CO2

If CaO is desired:

atom economy = 56.1 / 100.1 × 100% = 56.0%

Esterification

CH3COOH + C2H5OH ⇌ CH3COOC2H5 + H2O

If ethyl ethanoate is desired:

atom economy = 88.0 / (60.0 + 46.0) × 100% = 83.0%

Why atom economy matters

High atom economy can reduce raw-material use and waste treatment. However, chemists must also consider yield, rate, energy use, safety, cost, toxicity and reaction conditions.

Common exam traps

Do not confuse atom economy with percentage yield. Atom economy comes from the balanced equation; percentage yield comes from experimental data.
Only include the desired product in the numerator. Other products are by-products for this calculation.
Include stoichiometric coefficients. Multiply each Mr by its coefficient before adding mass contributions.
A high atom economy does not guarantee the best industrial process. Yield, rate, energy, safety and cost also matter.

Frequently asked questions

Can atom economy exceed 100%?

No. A value above 100% indicates incorrect data, an unbalanced equation or a missing reactant.

Why are reactant coefficients included?

Coefficients show how many formula units or moles take part, so they change the total mass contribution of each substance.

Do catalysts appear in the calculation?

Catalysts are not consumed overall, so they are not included as reactants in the atom economy calculation.

Can an addition reaction have 100% atom economy?

Yes. When all reactant atoms enter a single desired product, the atom economy is 100%.

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