# Nitrox MOD and EAD Calculator (Dive Kit): Free Nitrox Calculator for MOD, EAD, END, PPO₂ and Gas Density

_Last updated: 2026-10-30_

> A free nitrox calculator (also an EAD calculator) at https://divekit.app/tools/nitrox-mod-calculator/ that takes an EANx or trimix mix (O₂ %, He %) and a depth and returns the working MOD (PPO₂ 1.4), the deco MOD (PPO₂ 1.6), and the PPO₂, EAD, END, gas density and EADD at that depth, with the minimum breathable depth for a hypoxic mix. It runs the same @divekit/core code as the Dive Kit app's Gas Specs tool. Free, no account.

## What do MOD, EAD and END mean?

- **MOD** (maximum operating depth): the deepest a gas can go before its oxygen partial pressure passes a limit. Working MOD at 1.4 bar, deco MOD at 1.6 bar (at rest on a stop).
- **EAD** (equivalent air depth): the depth on air with the same nitrogen partial pressure. Used to read air tables for nitrox. About decompression, not narcosis.
- **END** (equivalent narcotic depth): how deep the mix feels for narcosis. Nitrogen only by default (then END equals EAD on nitrox); optionally oxygen counts as narcotic too. Helium lowers it.
- **Gas density**: how thick the gas is to breathe at depth, in g/L. **EADD** is the depth on air with the same density.

## Who is the nitrox MOD calculator best for?

- **Nitrox divers** checking how deep a fill can go at 1.4 and 1.6 bar, in metres or feet.
- **Technical divers** reading a trimix or deco gas at a depth: PPO₂, END and density with status colours.
- **Instructors** showing why EAD and END differ, and how helium and the O₂-narcotic convention move END.

## Formula

```latex
\mathrm{MOD} = m_\text{bar} \times \left( \frac{P_{\text{O}_2,\max}}{F_{\text{O}_2}} - P_\text{surf} \right), \qquad
\mathrm{EAD} = m_\text{bar} \times \left( \frac{F_{\text{N}_2}}{0.79} P_\text{amb} - P_\text{surf} \right), \qquad
P_\text{amb} = P_\text{surf} + \frac{d}{m_\text{bar}}
```

```latex
\rho_\text{surf} = 1.429 F_{\text{O}_2} + 1.251 F_{\text{N}_2} + 0.1786 F_\text{He}, \qquad
\rho = \rho_\text{surf} \times P_\text{amb} \times \frac{273.15}{273.15 + T}
```

P_surf is the surface pressure (1.01325 bar at sea level), m_bar the metres of water per bar for the water type (10.00 in EN 13319 water, the default), d the depth, T the water temperature (15 °C). The density constants are for 0 °C and 1 atm; the code multiplies them by the absolute pressure in bar as it stands (not converted to atm), so density reads about 1.3 % high.

## How does Dive Kit compute it?

- Depth converts to pressure from 1.01325 bar, not a round 1 bar, with the chosen water type: EN 13319, salt, fresh or Red Sea. MODs therefore sit a fixed 0.13 m shallower than the 10 m per bar rule of thumb in EN 13319 water ((1.01325 − 1) × 10.00 m), before flooring.
- A MOD is converted to feet from the unrounded metres, then floored to the whole metre or foot, so it never lies past the true MOD.
- Statuses: PPO₂ "within 1.4", "deco only" past 1.4 bar, "too high" past 1.6 bar (each with a 0.03 bar tolerance, the deco planner's gas-switch rule). Density "elevated" past 5.2 g/L and "too dense" past 6.2 g/L, judged at one decimal. A hypoxic mix (PPO₂ under 0.16 bar at the surface) shows its minimum depth.
- The answer bar shows the mix and its working MOD ("EANx32 · MOD 33 m") with a line on where it is breathable ("Breathable from the surface to 33 m at PPO₂ 1.4"). A status pill appears only when a limit is passed: "Deco only", "PPO₂ too high", "Hypoxic", "Hypoxic mix", "High gas density" or "Gas density too high".
- O₂ + He cannot pass 100 %: helium is lowered to fit and the page says so.
- Worked example (computed by the page at build time): EANx32 has a working MOD of 33 m (110 ft) and a deco MOD of 39 m (130 ft); at 30 m it reads PPO₂ 1.28 bar, EAD 24.4 m and 5.0 g/L.
- Static reference tables on the page: MOD in metres and feet for Air, EANx25 to EANx50, 80 % and oxygen at PPO₂ 1.2, 1.4 and 1.6; and EAD for EANx28, 32 and 36 from 18 to 40 m (a dash past the 1.4 bar working MOD).
- EAD by hand: EAD = m_bar × (F_N₂ ÷ 0.79 × P_amb − P_surf). EANx32 at 30 m: (0.68 ÷ 0.79 × 4.013 − 1.01325) × 10.00 = 24.4 m.

## How does it compare?

| | Dive Kit web calculator | Dive Kit app (Gas Specs) | Typical online MOD calculator |
|---|---|---|---|
| Outputs | Working and deco MOD, PPO₂, EAD, END, density, EADD, min depth | Same, plus no-stop time (NDL) | MOD, sometimes EAD |
| Trimix (helium) | Yes | Yes | Rarely |
| Surface pressure | 1.01325 bar, water type chosen | Same | Usually 1 bar, 10 m per bar |
| MOD rounding | Floored, feet from unrounded metres | Same | Varies |
| Status and warnings | PPO₂, density, hypoxia | Same | Rarely |
| Price | Free, no account | Free tool in the app | Free |

## Facts at a glance

- **Page:** https://divekit.app/tools/nitrox-mod-calculator/
- **Inputs:** O₂ % (5 to 100), He % (0 to 95), depth (1 to 300 m), water type, O₂ counted as narcotic (yes or no)
- **Outputs:** working MOD (1.4), deco MOD (1.6), PPO₂, gas density, EAD, END, EADD, minimum depth for hypoxic mixes, a status line and warnings
- **Units:** metric and imperial toggle; PPO₂ always in bar
- **Works without an account:** yes; the default result and the MOD table are in the page HTML
- **Same code as the app:** yes, @divekit/core `calculateEadPpo2` and `calculateMOD`
- **In the app:** the Gas Specs tool adds the no-stop time for the mix at depth; free on iOS and Android
- **Guide:** https://divekit.app/docs/tools/gas-specs/
- **Limits:** a planning aid, not a dive computer. It reads the mix you type in; analyse the real cylinder before diving.
- **Last updated:** 2026-10-30

## Sources

- GUE General Training Standards v10.4, section 2.2 (https://www.gue.com/files/Standards_and_Procedures/GUE-Standards-v10.4.pdf): planned PPO₂ at most 1.4 bar while working, 1.6 bar while resting; END at most 30 m (100 ft) with helium the only non-narcotic gas.
- InDepth, "Standard Gases" (https://indepthmag.com/standard-gases-the-advantages-of-having-everyone-singing-the-same-song/): GUE standard gases are designed for a working PPO₂ of 1.2 to 1.3 bar.
- Anthony and Mitchell (2016), Respiratory Physiology of Rebreather Diving (https://www.omao.noaa.gov/sites/default/files/documents/Rebreathers%20and%20Scientific%20Diving%20Proceedings%202016.pdf): 5.2 g/L ideal and 6.2 g/L maximum gas density.
- EN 13319:2000 (https://knowledge.bsigroup.com/products/diving-accessories-depth-gauges-and-combined-depth-and-time-measuring-devices-functional-and-safety-requirements-test-methods): the depth-gauge standard the default water type is named after (paywalled).

## Related

- [Best mix calculator for nitrox and trimix](https://divekit.app/tools/trimix-best-mix-calculator/): work out the mix for a depth
- [Gas blending calculator](https://divekit.app/tools/gas-blending-calculator/): blend the mix
- [Conventions](https://divekit.app/docs/engine/conventions/): surface pressure, water types and rounding