Respiratory Quotient Calculator
Calculate the respiratory quotient from carbon dioxide produced and oxygen consumed, and read off which fuel the body is mainly burning.
How it works
RQ = CO₂ produced ÷ O₂ consumed
The respiratory quotient is the ratio of carbon dioxide released to oxygen consumed during metabolism, and it reveals which fuel is being burned. Carbohydrates, with plenty of oxygen already in the molecule, give an RQ near 1.0; fats, which are oxygen-poor and need more inhaled oxygen to burn, give about 0.7; protein sits around 0.8. Values above 1.0 usually signal anaerobic metabolism or hyperventilation rather than a fuel mix.
Worked example
If a subject produces 200 mL of CO₂ while consuming 250 mL of O₂, the RQ is 200 ÷ 250 = 0.8 — the value typical of protein metabolism or a mixed fat-and-carbohydrate diet.
Sources: Respiratory quotient — Wikipedia
Frequently asked questions
What RQ corresponds to each fuel?
Roughly: pure carbohydrate ≈ 1.0, protein ≈ 0.8 and fat ≈ 0.7. A typical mixed diet gives an RQ around 0.8–0.85, and the value shifts as the body switches fuels during rest, exercise or fasting.
Why is fat's RQ lower than carbohydrate's?
Fat molecules contain little oxygen of their own, so burning them requires proportionally more inhaled oxygen for the same carbon dioxide released — pushing the CO₂/O₂ ratio down to about 0.7. Carbohydrates already carry oxygen, so they need less.
Can RQ exceed 1.0?
Yes, briefly. During intense exercise, extra CO₂ is blown off from buffering lactic acid, and hyperventilation adds more, so measured RQ can rise above 1.0. That reflects acid-base changes, not a fuel with more carbon than oxygen.
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Educational estimate, not medical advice — verify formulas, units and assumptions for your specific case.