Calculator inputs
Formula used
How to use this calculator
- Choose the calculation mode that matches your known values.
- Select a preset or enter your own measurements.
- Choose concentration, pressure, altitude, and temperature units.
- Select dry or humidified gas when applicable.
- Press calculate to view results and conversion tables.
- Copy, print, or export the completed calculation.
Understanding CO₂ partial pressure
Partial pressure measures one gas within a mixture. Dalton’s law links each fraction with total pressure. The method supports environmental and laboratory gas calculations accurately.
Humidity reduces the pressure available to dry gases. Water pressure depends strongly on the gas temperature. Correct humidity treatment improves respiratory gas calculations significantly today.
Altitude lowers atmospheric pressure as elevation increases. Equal CO₂ fractions then produce lower partial pressures. The comparison clarifies pressure changes across different elevations quickly.
Example data
| Example | CO₂ value | Total pressure | Condition | Approximate result |
|---|---|---|---|---|
| Outdoor air | 420 ppm | 1 atm | Dry | 0.319 mmHg |
| Indoor threshold example | 1,000 ppm | 1 atm | Dry | 0.760 mmHg |
| Laboratory incubator | 5% | 1 atm | Dry | 38.0 mmHg |
| Exhaled gas | 4% | 760 mmHg | Humidified at 37°C | 28.5 mmHg |
| Altitude example | 420 ppm | Estimated at 1,500 m | Dry | About 0.267 mmHg |
| Blood estimate | pH 7.40, HCO₃⁻ 24 | Not applicable | Henderson–Hasselbalch | About 40 mmHg |
Frequently asked questions
What is CO₂ partial pressure?
It is the pressure contributed by carbon dioxide within a gas mixture.
How is CO₂ partial pressure calculated?
Multiply the CO₂ mole fraction by the applicable total gas pressure.
Can I enter CO₂ in ppm?
Yes. The calculator converts ppm into a mole fraction automatically.
What changes for humidified gas?
Water-vapour pressure is subtracted before the CO₂ fraction is applied.
Why does altitude reduce partial pressure?
Atmospheric pressure falls with altitude, reducing each gas component’s pressure.
Is mmHg the same as torr here?
They are treated as equivalent for practical calculations in this tool.
Can the calculator work backwards?
Yes. Reverse mode calculates fraction, percentage, ppm, and ppb.
How is water-vapour pressure estimated?
The automatic option uses a Magnus saturation-pressure approximation from temperature.
What does the blood-gas mode calculate?
It estimates PaCO₂ from pH and bicarbonate using Henderson–Hasselbalch.
Can blood-gas results diagnose a condition?
No. The estimate cannot replace testing, clinical review, or medical advice.
Which pressure units are supported?
Pa, kPa, hPa, bar, mbar, atm, mmHg, torr, psi, and cmH₂O are included.