Input parameters
Example data table
The following examples illustrate typical nitrox partial pressures at different depths.
| Mix (FO2 %) | Depth (m) | Ambient pressure (bar) | PO2 (bar) | PN2 (bar) |
|---|---|---|---|---|
| 32 | 20 | 3.0 | 0.96 | 2.04 |
| 32 | 30 | 4.0 | 1.28 | 2.72 |
| 36 | 28 | 3.8 | 1.37 | 2.43 |
Formula used
The calculator uses Dalton's law of partial pressures. Total ambient pressure at depth is approximated as:
- For meters: Pambient = Psurface + depth / 10
- For feet: Pambient = Psurface + depth / 33
The oxygen fraction is FO2 = O2% / 100. The partial pressures are then:
- PO2 = FO2 × Pambient
- PN2 = (1 - FO2) × Pambient
For convenience, partial pressures are reported in bar and converted to kilopascals by multiplying by 100.
How to use this calculator
- Choose your nitrox mix by entering the oxygen percentage (FO2).
- Enter the planned maximum depth and select meters or feet.
- Set surface pressure, typically 1.0 bar at sea level.
- Click Calculate to compute ambient and partial pressures.
- Review the safety note regarding PO2 thresholds at your selected depth.
- Download the results as CSV or a simple PDF summary if required.
Always confirm calculations with dive tables, training materials, and dive computer recommendations before planning real dives.
Nitrox partial pressure article
Understanding nitrox partial pressure
Nitrox is a breathing gas where the oxygen fraction is higher than in air. Instead of twenty-one percent oxygen, common nitrox mixes use twenty-eight to forty percent. Raising oxygen reduces nitrogen load, but increases oxygen partial pressure, which must always remain within safe limits during a dive.
Depth, ambient pressure, and gas fractions
As a diver descends, ambient pressure increases roughly one bar for every ten meters in seawater. Dalton's law states that each gas contributes a fraction of this total pressure. For nitrox, oxygen and nitrogen share the total ambient pressure according to their fractions in the breathing mixture.
Safe oxygen exposure limits in practice
Many training agencies suggest a working limit around one point four bar for oxygen partial pressure. A contingency limit of one point six bar is sometimes referenced. This calculator highlights when your chosen mix and depth exceed these thresholds, encouraging more conservative choices for everyday recreational nitrox diving.
Connections with other gas property tools
Understanding partial pressure fits naturally alongside other gas property calculations. For example, vapor pressure modelling with the Vapor Pressure from Antoine Calculator helps describe how liquids evaporate into gaseous phases. Together, these tools build intuition about how gases and vapors behave under differing temperature and pressure conditions.
Relating partial pressure to gas composition
When planning advanced dives, composition and molecular properties matter. The Molar Mass of Gas Calculator helps characterize individual gases used in custom mixtures. Combining molar mass information with partial pressure results supports better predictions of gas density, narcotic potential, and breathing resistance under pressure.
Using the calculator for dive planning
Divers can use this nitrox partial pressure calculator alongside dive computers and tables. First, select the planned mix. Next, explore how changing depth influences oxygen partial pressure. Small adjustments often keep PO2 within conservative ranges while still decreasing nitrogen exposure compared with air, improving decompression efficiency and comfort after the dive.
Limitations, assumptions, and safety reminders
This calculator assumes seawater conditions and simplified depth to pressure conversions. Real environments, equipment, and physiology introduce additional uncertainties. Always follow your training, apply manufacturer guidance, and verify results with multiple tools. Ultimately, thoughtful planning, progressive experience, and conservative limits provide the strongest foundation for safe, enjoyable nitrox diving.
Frequently Asked Questions
1. What does this nitrox partial pressure calculator compute?
It calculates ambient pressure at depth and the resulting oxygen and nitrogen partial pressures for a chosen nitrox mix, helping you evaluate whether planned dives stay within accepted exposure limits.
2. Which units can I use for depth?
You can enter depth in meters or feet. The calculator converts either unit into an approximate ambient pressure, using ten meters per bar or thirty-three feet per bar respectively for seawater.
3. Why is oxygen partial pressure important for nitrox diving?
Higher oxygen fractions reduce nitrogen loading but increase oxygen partial pressure. Excessive PO2 dramatically raises the risk of oxygen toxicity. Monitoring PO2 keeps dives within training guidelines and supports safer gas and depth selections.
4. Can I use this calculator for trimix or other gases?
This tool is designed for nitrox, containing only oxygen and nitrogen. For trimix or additional gases, you would need a calculator that handles three or more gas fractions and tracks their individual partial pressures.
5. Does the calculator replace my dive computer?
No. It is an educational and planning aid, not a life support device. Always follow your dive computer, training organization procedures, instructor advice, and manufacturer recommendations when planning or executing dives.
6. How accurate are the depth to pressure conversions?
The conversions use standard approximate relationships suitable for many planning purposes. Local salinity, temperature, or equipment considerations can change actual pressures slightly, so always treat outputs as estimates, not exact measured values.