Atom Economy Calculator

Find the atom economy of a reaction from reagent and product masses.

Supports up to six reagents with metric and imperial mass units.

Updated August 24, 2026

CreatorFrank Zhao

Loading calculator…

What is atom economy?

Atom economy measures how efficiently a chemical reaction converts reactant atoms into the desired product. Unlike percent yield, which tells you how much product you actually recovered, atom economy tells you how much of the starting material could end up in the product if the reaction were perfectly selective.

A reaction with 100% atom economy incorporates every atom from the reagents into the target molecule. In practice, most reactions produce by-products — salts, water, leaving groups — so atom economy is almost always below 100%. The lower the atom economy, the more waste the reaction generates per kilogram of product.

Why it matters: atom economy is one of the 12 Principles of Green Chemistry. Designing reactions with high atom economy reduces waste at the source, lowering disposal costs and environmental impact.

How to use this calculator

This calculator supports two input modes. Pick the one that matches the data you have available.

Mode 1 — I know the masses

Use this when you have measured the actual masses of reagents and product in the lab.

Select the masses under "I know..."
Choose the number of reagents (1–6) from the dropdown
Enter each reagent mass and the desired product mass
The total reagent mass and atom economy compute automatically

Mode 2 — I know the molecular weight

Use this when you are designing a reaction on paper and know the balanced equation but have not yet run the experiment.

Select the molecular weight under "I know..."
Choose the number of reagents (1–6)
Enter each reagent's stoichiometric coefficient and molecular weight, plus the product coefficient and molecular weight
The weighted total and atom economy compute automatically

Bidirectional calculation

You can enter any combination of fields and leave the rest blank — the calculator solves for the missing values. For example, enter the total reagent mass and atom economy to find the product mass, or enter the product mass and atom economy to find the total.

Worked example — masses mode

A reaction uses two reagents: 10 g of sodium carbonate and 20 g of hydrochloric acid. The desired product (sodium chloride) has a mass of 15 g. What is the atom economy?

m_{\text{total}}

=

10 + 20

=

30\ \text{g}

\text{AE}

=

\frac{m_{\text{product}}}{m_{\text{total}}}

=

\frac{15}{30}

=

50\%

Half of the reactant atoms end up in the desired product; the other half become waste.

Worked example — molecular weight mode

In a balanced equation, reagent A (coefficient 1, molecular weight 16 g/mol) reacts with reagent B (coefficient 1, molecular weight 18 g/mol) to form a product (coefficient 1, molecular weight 28 g/mol).

w_{\text{total}}

=

(1 \times 16) + (1 \times 18)

=

34\ \text{g/mol}

\text{AE}

=

\frac{c_p \cdot w_p}{w_{\text{total}}}

=

\frac{1 \times 28}{34}

=

82.35\%

About 82% of the molecular mass is incorporated into the product. The remaining 18% becomes by-products.

Formula and variables

The calculator uses two equivalent formulas depending on which input mode you select.

Masses mode

\text{AE} = \frac{m_{\text{product}}}{\sum_{i=1}^{n} m_i} \times 100\%

Molecular weight mode

\text{AE} = \frac{c_p \cdot w_p}{\sum_{i=1}^{n} c_i \cdot w_i} \times 100\%

Symbol	Meaning
$\text{AE}$	Atom economy (0–100%)
$m_i$	Mass of reagent i (masses mode)
$m_{\text{product}}$	Mass of the desired product (masses mode)
$c_i$	Stoichiometric coefficient of reagent i from the balanced equation
$w_i$	Molecular weight of reagent i (MW mode)
$c_p,\ w_p$	Coefficient and molecular weight of the desired product
$n$	Number of reagents (1–6)

Key difference between the two modes

Masses mode uses measured experimental masses — it reflects what actually happened in the flask. Molecular weight mode uses stoichiometric masses (coefficient × molar mass) — it reflects the theoretical maximum from the balanced equation. Both give the same atom economy for the same reaction, but the MW mode is useful during reaction design before any experiment is run.

Real-world examples

Aspirin synthesis

Salicylic acid reacts with acetic anhydride to produce aspirin and acetic acid as a by-product.

\text{AE} = \frac{180}{180 + 60}

=

75\%

25% of reactant atoms become acetic acid waste.

Diels-Alder reaction

Butadiene adds to ethylene in a single step with no by-products — every atom ends up in the product.

\text{AE} = 100\%

An ideal example of a 100% atom-economical reaction.

Grignard reaction

Phenylmagnesium bromide reacts with CO₂ to form benzoic acid. The magnesium salt by-product lowers atom economy.

\text{AE} \approx 46\%

Over half the reactant mass ends up as magnesium salt waste.

Hydrogenation of ethylene

Ethylene plus hydrogen yields ethane — an addition reaction with no leaving groups.

\text{AE} = 100\%

Addition reactions typically achieve 100% atom economy.

Frequently asked questions

How is atom economy different from percent yield?

Atom economy measures how many atoms from the reactantscan end up in the product based on the balanced equation. Percent yield measures how much product youactually isolated. A reaction can have 100% atom economy but only 40% yield if side reactions or losses occur during work-up.

Should I always aim for 100% atom economy?

High atom economy is desirable, but it is one factor among many. A reaction with 70% atom economy that runs at room temperature with a cheap catalyst may be greener overall than a 100% atom-economy reaction that requires extreme conditions or expensive reagents.

Why does the molecular weight mode ask for stoichiometric coefficients?

The total molecular weight is a weighted sum: $\sum c_i \cdot w_i$ . Without coefficients, you cannot correctly account for reactions where multiple moles of one reagent react with a single mole of another.

Can I use this calculator for catalytic reactions?

Yes — include the catalyst as one of the reagents with its coefficient and molecular weight. Note that catalysts are regenerated and not consumed, so the resulting atom economy may not fully reflect the true waste profile. For a more complete picture, consider the

Limitations

Theoretical only. Atom economy is a stoichiometric calculation — it does not account for reaction conditions, catalysts, solvents, or actual yields.

Up to 6 reagents. If your reaction involves more than 6 reagents, you can group minor reagents or catalysts into a single entry for a simplified estimate.

Non-negative inputs only. Masses and molecular weights must be zero or positive. Stoichiometric coefficients must be at least 1.

Does not replace percent yield. High atom economy is necessary but not sufficient for a green process. A reaction can have excellent atom economy but poor yield if conversion or selectivity is low.

Related Calculators

Atom Calculator

Calculate atomic properties including protons, neutrons, electrons, atomic number and mass number

Try Now

Electron Configuration Calculator

Get the electron configuration for any element from the periodic table. View atomic number, atomic mass, and valence electrons.

Try Now

Atomic Mass Calculator

Calculate atomic mass from protons and neutrons. Get atomic mass in various units including atomic mass units (u), kilograms, and more.

Try Now

Electronegativity Calculator

Calculate electronegativity difference between two elements and determine bond type (ionic, polar covalent, or nonpolar covalent).

Try Now

Average Atomic Mass Calculator

Calculate the average atomic mass of an element based on the isotopes and their natural abundances.

Try Now

Mass Concentration to Molar Concentration Conversion

Convert mass concentration (g/L, kg/L, mg/L) to molar concentration (M, mM, μM) and vice versa using molar mass.

Try Now