---
title: "Units and rounding"
description: "The units DiveLogic works in, and which direction each number is rounded so that the figure you read is the cautious one."
---

> Documentation Index
> Fetch the complete documentation index at: https://docs.divelogic.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# Units and rounding

DiveLogic is metric everywhere. There is no imperial option, no unit setting and
nothing to convert.

| Quantity | Unit | Written as |
|---|---|---|
| Depth | metres | `45 m` |
| Time | minutes | `25 min` |
| Pressure | bar | `1.4 bar` |
| Volume | litres | `2400 L` |
| Gas fraction | percent | `21 %`, `21/35` |
| Gas density | grams per litre | `5.2 g/L` |
| Descent and ascent rate | metres per minute | `9 m/min` |
| Breathing rate | litres per minute | `15 L/min` |
| Temperature | degrees Celsius | `12 °C` |
| Altitude | metres above sea level | `1200 m` |

Pressures are absolute, not gauge: `1 bar` is the surface, not zero. Depth
becomes pressure from the weight of the water above you, at 1025 kg/m³ for salt
and 1000 kg/m³ for fresh, on top of the atmospheric pressure at your altitude.
The `1 + depth ÷ 10` shortcut is not used anywhere, so a plan at 30 m in fresh
water is not the same plan as one at 30 m in the sea. See
[Environment](/planning/environment).

## Which way numbers round

| Number | Rounds | So that |
|---|---|---|
| Maximum operating depth | **Down**, to the whole metre | The depth limit you read is never deeper than the one the gas actually has. A MOD of 33.7 m is shown as 33 m. |
| Any other depth limit from a ppO₂ | **Down** | Same reason. |
| Narcotic depth (END and EAD) | **Up** | A deeper narcotic depth is the stricter judgement of a mix. |
| Decompression ceiling | **Up** | A shallower ceiling would invite you to come up further than the model allows. |
| Stop depths | **Up**, onto your stop spacing | A stop sits at or below the ceiling, never above it. |
| Runtime and time to surface | To the nearest minute | These are summaries, not limits. |

The first stop is the exception: the ceiling at the moment you leave the bottom
is taken to the next stop depth *toward the surface*, and GF Low supplies the
margin there. See [Gradient factors](/theory/gradient-factors).

A ceiling is rounded before it meets the stop grid, so a ceiling of 3.09 m lets
you sit at the 3 m stop. All of this rounding is display only; the schedule is
computed on the unrounded numbers throughout.

## Read next

- [Every setting](/reference/plan-fields) lists every value you can enter, with
  its unit.
- [Every number the planner gives you](/reference/outputs) does the same for
  every value you read back.
- [Gas density](/theory/gas-density) is where the g/L thresholds come from.

Source: https://docs.divelogic.ai/reference/units/index.mdx