What this calculator does
Atom economy is the share of reactant mass that the reaction is designed to place in the desired product. A reaction giving a 44.05 g/mol product alongside water at 18.02 has an atom economy of 71.0%.
It is a property of the reaction equation, not of how well the reaction was run. A synthesis can achieve 100% yield and still have poor atom economy if the stoichiometry inherently discards most of the mass as by-product. Improving yield is a matter of technique; improving atom economy requires a different reaction.
The formula
The molar mass of the desired product is divided by the sum of the molar masses of all products, then multiplied by 100. Because mass is conserved, the total product mass equals the total reactant mass, so this is equivalent to the share of reactant mass ending up where you want it. Addition reactions score 100% by definition, since they have no by-products.
| Term | Meaning |
|---|---|
| Atom economy | Desired product mass over total product mass, as a percentage. |
| Green chemistry | The framework this measure comes from, introduced by Trost in 1991. |
| Addition reaction | All reactants combine into one product, giving 100% atom economy. |
| E-factor | A related measure: mass of waste per mass of product, which counts solvents too. |
The inputs explained
| Field | What to enter |
|---|---|
| Molar mass of desired product (g/mol) | Molar mass of the desired product. |
| Molar mass of each by-product (comma-separated) | Molar mass of each by-product, comma separated. Enter 0 if there are none. |
When to use it
Comparing synthetic routes
Two routes to the same product can differ enormously in how much mass they discard.
Assessing environmental impact
Waste that a reaction produces by design is waste that no amount of optimisation will remove.
Teaching green chemistry
Atom economy is the clearest illustration of why yield alone is an incomplete measure of efficiency.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How much does by-product mass cost?
The same product with different by-product loads.
| By-product molar masses | Atom economy | Total product molar mass | By-product mass wasted |
|---|---|---|---|
| none | 100.0% | 44.05 g/mol | 0.00 g/mol |
| 18.02 | 71.0% | 62.07 g/mol | 18.02 g/mol |
| 44.05 | 50.0% | 88.10 g/mol | 44.05 g/mol |
| 18.02, 18.02 | 55.0% | 80.09 g/mol | 36.04 g/mol |
Questions
What is the difference between atom economy and percent yield?
Atom economy is a property of the reaction equation: how much of the reactant mass the stoichiometry directs into the desired product. Percent yield measures how much of that theoretical maximum a particular run actually achieved. A reaction can be 100% yielding and 40% atom economical.
Which reactions have 100% atom economy?
Addition reactions, where all reactants combine into a single product with nothing left over. Hydrogenation of an alkene is the standard example. Substitution and elimination reactions always score below 100% because they produce something alongside the target.
Does atom economy account for solvents?
No, and that is its main limitation. Solvents, catalysts and workup reagents are often the largest mass in a process and are entirely excluded. The E-factor, mass of waste per mass of product, captures them and usually gives a far less flattering picture.
Why does green chemistry care about this?
Because waste produced by design cannot be optimised away. A reaction that discards half its mass as by-product will always do so, however well it is run. Choosing routes with high atom economy prevents waste rather than treating it afterwards.
For how well a run performed, see the percent yield calculator. For the maximum obtainable, see the theoretical yield calculator.