# Air consumption calculation

The aim of an **air consumption calculation** is to determine, as part of the dive planning, which amount of air is necessary for the dive and which size of diving cylinder must be used.

Likewise, it can also be checked whether the planned diving time can be reached with the existing diving cylinder or how long the existing diving cylinder can be used to dive to the planned depth.

## Basic knowledge for Open Water Diver* (OWD*)

### Calculation

For the calculations, it is usually sufficient if you assume a surface air consumption of 20 l/min. However, if you have determined a significantly higher SAC during your previous dives, use this value.

The air consumption during the planned dive can be estimated as shown below. Please note that the dive time must already include ascent, deco and safety stops.

- [math]\text{air consumption} = \text{SAC} \cdot \text{ambient pressure} \cdot \text{dive time}[/math]

- Example 1: 20-minute dive at 20 m

- [math]\text{air consumption} = 20\ l/min \cdot 3\ bar \cdot 20\ min = 1200\ barl[/math]
- A 10 l cylinder has an air supply of 1500 barl. This leaves air to spare and the dive is possible.

- Example 2: 30-minute dive at 20 m

- [math]\text{air consumption} = 20\ l/min \cdot 3\ bar \cdot 30\ min = 1800\ barl[/math]
- A 10 l cylinder
*only*has an air supply of 1500 barl. So the dive is*not*possible.

The possible dive time is calculated with the known SAC as follows:

- [math]\text{dive time} = \frac{\text{air supply}}{\text{SAC} \cdot \text{ambient pressure}}[/math]

- For the above Example (10 l cylinder at a depth of 20 m):

- [math]\text{dive time} = \frac{1500\ barl}{20\ l/min \cdot 3\ bar} = 25\ min[/math]