---
title: "Gas needed"
description: "Checking whether a cylinder covers a stretch of diving at one constant depth, from your RMV and your cylinder."
---

> 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.

# Gas needed

import { GasNeededScreen } from "@/components/react/ToolScreens";

Gas needed answers *will my cylinder last this dive?* It works out the gas you
breathe at one depth for a set time and takes it from your cylinder. It is a
quick check of a stretch of diving, not a gas plan.

## What you enter

- **Depth** (m) and **Time** (min): the stretch of dive, held at that depth
  throughout.
- **RMV** (L/min): your surface-equivalent breathing rate. Measure it with
  [RMV from a dive](/tools/rmv-from-a-dive).
- **Water**: **Salt** or **Fresh**.
- **Size, each** (L), **Start** (bar) and **Cylinders** (**Single** or
  **Twin**): your cylinder. Twin doubles the gas at the same pressure.

The **Breathing** and **Cylinder** fields are shared with Turn pressure and
Minimum gas, so a change here shows there too.

## Reading the result

- **Gas needed** (L): the main figure. Its rail shows the pressure used against
  a solid mark at your full **Start** pressure, and turns red when the dive
  needs more than the cylinder holds.
- **Pressure used** (bar): the same gas as a gauge drop.
- **Left** (bar) and **Left** (%): what the gauge reads at the end. The bar
  figure turns red when it goes below zero.

With gas to spare, the verdict reads, for example, *Leaves 108 bar. Check that
covers your ascent and reserve with Minimum gas.* Without, it reads *Not enough
gas*, with what the dive needs and what the cylinder holds.

## What it leaves out

The method note says it plainly: this is gas breathed at one constant depth for
the whole time.

- **No descent, ascent or stops.** The gas to get down and back up is not
  counted.
- **No reserve.** Gas left at the end is not gas you can spend. Work out what to
  keep with [Minimum gas](/tools/minimum-gas).
- **No stress.** The RMV is your relaxed rate throughout.

For a whole dive, with every level, stop and gas, build a plan in the planner.

## Next

- [Turn pressure](/tools/turn-pressure) sets when to end the outbound leg.
- [Gas use in a plan](/gases/consumption) covers the same question for a whole
  dive.

Source: https://docs.divelogic.ai/tools/gas-needed/index.mdx