Calculator Inputs
Large screens show 3 columns, smaller screens show 2, and mobile shows 1.
Example Data Table
These worked examples show dry and humid calculations in standard chemistry-style conditions.
| Scenario | Total Pressure (kPa) | Oxygen Fraction | Water Vapor Pressure (kPa) | Oxygen Partial Pressure (kPa) |
|---|---|---|---|---|
| Dry air at sea level | 101.325 | 0.2095 | 0 | 21.2276 |
| Humid air at 37°C | 101.325 | 0.2095 | 6.2599 | 19.9161 |
| Nitrox 32 at 2 atm | 202.65 | 0.32 | 0 | 64.848 |
| 40% oxygen at 150 kPa, humid 25°C | 150 | 0.4 | 3.1579 | 58.7368 |
Formula Used
Dalton’s law: P(O2) = x(O2) × P(effective)
Oxygen mole fraction from moles: x(O2) = n(O2) ÷ n(total)
Humid gas correction: P(effective) = P(total) − P(H2O)
Solve oxygen fraction: x(O2) = P(O2) ÷ P(effective)
Solve total pressure: P(total) = [P(O2) ÷ x(O2)] + P(H2O)
When auto humidity is selected, the page estimates water vapor pressure from temperature using a standard vapor-pressure equation for water.
How to Use This Calculator
- Select whether you want oxygen partial pressure, oxygen fraction, or total pressure.
- Choose how you want to describe oxygen composition: fraction, percentage, or moles.
- Enter known pressures and choose the correct pressure unit.
- Pick dry gas or humid gas correction.
- For humid gas, enter temperature or a manual water vapor pressure.
- Choose an output unit and optional chart range.
- Press Calculate to show the result above the form.
- Use the CSV and PDF buttons to save your report.
FAQs
1) What is oxygen partial pressure?
Oxygen partial pressure is the share of total gas pressure produced by oxygen alone. It equals oxygen fraction multiplied by the effective gas pressure.
2) Why does humidity matter here?
Water vapor takes part of the total pressure. In humid gas, oxygen acts only on the remaining dry-gas pressure, so the available oxygen pressure becomes lower.
3) Can I enter oxygen as a percentage?
Yes. You can enter oxygen either as a percentage, a decimal fraction, or from oxygen moles divided by total moles.
4) What law does this calculator use?
It uses Dalton’s law of partial pressures. For humid calculations, it first subtracts water vapor pressure, then applies the oxygen fraction.
5) When should I use dry gas mode?
Use dry gas mode when the mixture contains negligible water vapor, or when your pressure data already excludes vapor pressure.
6) Why can the solved oxygen fraction exceed 100%?
That means the chosen oxygen partial pressure is too high for the entered total pressure and humidity. Recheck units, totals, and vapor correction.
7) Which units are supported?
This page accepts and converts kPa, atm, mmHg, bar, and psi. Use the same input unit for manual vapor pressure values.
8) What does the graph show?
The graph shows how oxygen partial pressure changes with total pressure, or how much oxygen percentage is required to hit a target value.