What this calculator does
Stoichiometric air-fuel ratio works out theoretical air-to-fuel mass ratio for complete combustion of a CxHy hydrocarbon. Enter your own figures above and the answer updates as you type: nothing is fixed in the code, so the result reflects exactly the numbers you supply.
The formula this calculator evaluates is printed under the tool and explained below, so you can check the working by hand or reuse it in a spreadsheet.
The formula
FormulaCαHβ + a(O2+3.76N2) → bCO2 + cH2O + dN2, a = α+β/4; AFR = a×(1×32+3.76×28.02) / (12.011α+1.008β)
The inputs explained
| Field | What to enter |
|---|---|
| Carbon atoms (α) | A number. Starts at 8. |
| Hydrogen atoms (β) | A number. Starts at 18. |
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 the answer changes with carbon atoms (α)
Every other input is held at the calculator’s starting values while carbon atoms (α) varies. Select any row to load that scenario into the calculator.
How the answer changes with carbon atoms (α)