Atom Economy Calculator
Atom economy percent and waste from molar masses.
What it does
Atom economy grades reactions by atoms kept: wanted product mass over all reactant mass, as a percent. High scores mean little waste by design, before yield or solvents enter. This page runs that ratio from three molar masses.
The default mirrors esterification shape: 60 plus 46 of reactants with 88 of wanted ester. Total is 106, economy is 83%, and waste is 17%. Water as co product is the waste here even though it ships elsewhere.
Economy differs from yield. Yield counts how much of the plan ran, while economy counts how much of the plan could ever land in product. A 100% yield on a 40% economy route still throws most atoms.
Use this to compare routes early. Addition beats substitution, rearrangements beat eliminations, and catalysis trims stoichiometric waste before a flask warms.
How to use
- Enter reactant A molar mass.
- Enter reactant B molar mass.
- Enter wanted product molar mass.
- Read economy first, then waste.
- Multiply by yield for real use.
Formula
- MW A
- Molar mass of first reactant.
- MW B
- Molar mass of second reactant.
- MW P
- Molar mass of wanted product.
Molar masses in g per mol from formulas or tables. Desired product only counts; co products are waste by this metric even when sold. Real efficiency multiplies economy by yield and divides by excess reagents.
Worked example
Example: 83% route
Reactants 60 and 46, wanted product 88 (esterification shape).
- Total: 60 + 46 = 106 g/mol.
- Economy: 88 / 106 x 100 = 83%.
- Waste: 100 - 83 = 17%.
- Check: 83 + 17 = 100%.
- Tool shows 83%, 17%, 106 g/mol.
Reference table
| Route | Math | Score |
|---|---|---|
| Addition 36 to 36 | 36/36 | 100% |
| Ester shape 88/106 | 88/106 | 83% |
| Half kept 30/60 | 30/60 | 50% |
| Quarter kept 25/100 | 25/100 | 25% |
Limits
- Design metric only. No yield or excess.
- Two reactants per pass.
- Solvents, energy, toxicity excluded.
- Co products counted as waste.
Common mistakes
- Mixing yield with economy.
- Counting co products as wanted.
- Using grams instead of molar masses.
- Forgetting excess reagent mass.
- Reading 100% as zero impact.
Try it yourself
Quick checks. Answers sit tucked under each question.
H2 4 plus O2 32 to water 36?
100%, 0% waste (36/36).
Reactants 60 total, product 30?
50% (30/60), waste 50%.
Questions
Atom economy?
Product over reactants total, times 100. Here 83%.
Waste share?
The rest to 100. Here 17%.
Perfect score?
100% when all reactant atoms land in product.
Yield included?
No. Yield multiplies economy for real mass use.
Green score alone?
No. Solvents and energy sit outside atom math.
Over 100%?
Product cannot top reactants. Check masses.