About

Human respiration produces carbon dioxide as a metabolic byproduct. An average adult at rest exhales approximately 200 mL CO₂/min, scaling to roughly 900 g/day or 330 kg/year. This rate is not constant. It varies with body mass (m), metabolic equivalent of task (MET), age-related basal metabolic decline, and altitude-driven ventilation changes. Errors in estimating personal CO₂ output lead to flawed carbon auditing in building ventilation design (ASHRAE 62.1 uses 0.0084 L/s per person as a baseline) and indoor air quality modeling. This calculator applies physiological constants from respiratory science to compute VCO₂ across activity states.

The tool approximates CO₂ production assuming standard atmospheric pressure and a respiratory quotient (RQ) of 0.83, typical of a mixed diet. Results are converted to mass using the ideal gas law at STP. Note: individual variation due to fitness level, body composition, and diet macronutrient ratio can shift actual values by ±15%. Pro tip: ventilation engineers should use sedentary rates for office calculations, not averages that include exercise periods.

Formulas

The volume of CO₂ exhaled is derived from the basal CO₂ production rate scaled by body mass, activity intensity, and correction factors:

V_CO₂ = r_base × m × MET × f_alt × f_age × t

Where V_CO₂ = total CO₂ volume in mL, r_base = 2.86 mL/min/kg (resting CO₂ production rate at RQ = 0.83), m = body mass in kg, MET = metabolic equivalent of the selected activity, f_alt = altitude ventilation correction factor, f_age = age-related metabolic correction factor, and t = duration in minutes.

Mass conversion uses the ideal gas law at STP:

mass_CO₂ = V_CO₂22400 mL/mol × 44 g/mol

Where 22400 mL/mol is the molar volume at STP and 44 g/mol is the molar mass of CO₂ (12 + 16 × 2).

Reference Data

Activity	MET Value	VCO₂ mL/min/kg	CO₂ per hour (70 kg) g/h	Example
Sleeping	0.9	2.57	21.2	Deep sleep, supine
Resting / Seated	1.0	2.86	23.6	Watching TV, reading
Light Office Work	1.5	4.29	35.4	Typing, desk work
Standing / Light Activity	2.0	5.72	47.2	Cooking, slow walking
Walking (4 km/h)	3.0	8.58	70.8	Casual stroll
Brisk Walking (6 km/h)	4.0	11.44	94.4	Commuting on foot
Cycling (moderate)	6.0	17.16	141.6	15-20 km/h pace
Swimming (moderate)	7.0	20.02	165.2	Freestyle, steady
Jogging (8 km/h)	8.0	22.88	188.8	Moderate jog
Running (10 km/h)	10.0	28.60	236.0	Steady run
Running (12 km/h)	11.5	32.89	271.4	Fast run
Sprinting	15.0	42.90	354.0	Near-max effort
Heavy Weightlifting	6.0	17.16	141.6	Compound lifts
Yoga / Stretching	2.5	7.15	59.0	Hatha yoga
Dancing (moderate)	5.0	14.30	118.0	Social dancing
Rowing (vigorous)	12.0	34.32	283.2	Competitive rowing
Soccer / Basketball	8.0	22.88	188.8	Recreational match
Climbing Stairs	9.0	25.74	212.4	Continuous stair climb
Housework (vigorous)	3.5	10.01	82.6	Scrubbing, mopping
Gardening	4.0	11.44	94.4	Digging, weeding

Frequently Asked Questions

CO₂ production scales linearly with metabolic mass. A person weighing 90 kg produces roughly 28.6% more CO₂ at rest than a 70 kg individual, because more tissue requires more oxygen consumption and thus generates more CO₂. The calculator uses r_base × m to capture this direct proportionality.

At higher altitudes, reduced partial pressure of oxygen triggers hyperventilation as a compensatory mechanism. While the total CO₂ produced metabolically stays similar, ventilation rate increases by approximately 5% at 1500 m and up to 25% at 4000 m during acclimatization. The calculator applies an altitude correction factor f_alt that ranges from 1.0 to 1.30.

Yes. Pure carbohydrate oxidation yields RQ = 1.0, fat oxidation yields RQ = 0.7, and protein yields roughly 0.8. This calculator assumes a mixed diet with RQ = 0.83. A ketogenic (high-fat) diet would reduce actual CO₂ output by approximately 10 - 15% compared to a high-carbohydrate diet.

An average adult exhales approximately 330 kg CO₂/year. A typical passenger car emits about 4600 kg CO₂/year (driving 20000 km at 230 g/km). Human breathing thus represents roughly 7% of one car's annual output. Critically, exhaled CO₂ is biogenic (recycled from food that absorbed atmospheric CO₂), so it does not add net carbon to the atmosphere.

Basal metabolic rate declines with age due to loss of lean muscle mass and reduced cellular metabolic activity. After age 40, BMR drops by roughly 2 - 3% per decade. Children and adolescents have higher per-kg metabolic rates due to growth processes. The calculator applies age correction factors from 1.20 (children) down to 0.75 (elderly over 80).

Yes, with caveats. ASHRAE Standard 62.1 specifies outdoor air rates partially based on occupant CO₂ generation. The standard assumes a sedentary adult produces about 0.0084 L CO₂/s. This calculator's resting rate for a 70 kg adult yields 0.0033 L/s, which represents pure metabolic production. ASHRAE values include safety margins. For gym or sports facility ventilation, use the exercise-level MET values from this tool.