PoolDose How to calculate pool volume in gallons or litres
Area times average depth gives the volume. A rectangle 8 m by 4 m at 1.5 m deep holds 48 m³, which is 48,000 litres. The Volume screen handles five shapes and a sloped floor, and passes the result on to Dosing.
Why does the volume matter so much?
Every dose in the app is proportional to the volume, so a pool that is 25% bigger on paper gets 25% too much product. A common cause is taking a sloped pool's depth at the deep end.
Which formulas does the app use for each shape?
- Rectangular: length × width × average depth.
- Oval: π × (length ÷ 2) × (width ÷ 2) × average depth.
- Round: π × (diameter ÷ 2)² × average depth.
- Kidney: length × width × average depth × 0.85. The 0.85 is a rule of thumb for the curves, not a measured shape.
- Stepped bottom: length × width × the average depth you type. The app does not model the steps.
With Sloped bottom on, the average depth is the shallow end plus the deep end, divided by two. That is right for a floor that slopes in a straight line and a little high if the deep part is short.
How do I measure the pool?
- Measure length and width at the water line, inside the walls, not to the outer edge of the coping.
- Measure depth from the water surface down, not from the pool edge. Water level is usually a few centimetres or inches below the coping.
- For a sloped floor, take the shallow end and the deep end, not the deepest spot you can find. If the floor has a flat part and a slope, a single average is only a guess.
- Use one unit throughout. Mixing metres and feet in one calculation is the quickest way to be out by a factor of three.
How do I work it out in PoolDose?
- Open Calculator > Volume.
- Choose the Shape.
- Type the length and width (or diameter) under Measurements.
- Either type one depth, or switch on Sloped bottom and fill in the shallow and deep end depths.
- Check the Result, then tap Use this volume. The button then reads Volume ready to use.
| Shape | Volume |
|---|---|
| Rectangular, one depth | 48.00 m³ (48,000 l) |
| Rectangular, sloped 1.2 m to 2.0 m (average 1.6 m) | 51.20 m³ |
| Same pool measured at the deep end only (2.0 m) | 64.00 m³, which is 25% too high |
| Oval | 37.70 m³ |
| Round, 5 m across | 29.45 m³ |
| Kidney | 40.80 m³ |
| Stepped bottom, average depth 1.3 m | 41.60 m³ |
In US units the same logic applies. A 26 ft by 13 ft pool, 5 ft deep, comes to about 12,642 gallons (47.86 m³). Type feet and the app converts them to metres before it does the maths. To turn cubic metres into US gallons yourself, multiply by 264.17: the 48 m³ rectangle above is about 12,680 gallons.
| Shape and size | Volume |
|---|---|
| Oval, 24 ft by 12 ft, 4.5 ft deep | 7,614 gal |
| Round, 16 ft across, 4 ft deep | 6,016 gal |
| Kidney, 30 ft by 15 ft, 4.5 ft deep | 12,876 gal |
| Rectangular, 33 ft by 16 ft, sloped 4 ft to 6.5 ft | 20,736 gal |
The volume you set here is the one Dosing and Assistant start from, until you type another in their own volume field. Until you set one, the app assumes 50 m³, so check it before you dose.
What are the usual mistakes?
- Using the deepest point as the depth of a sloped pool. In the example that adds 25% to every dose.
- Forgetting to tap Use this volume. Dosing and Assistant then keep the old value, or the 50 m³ placeholder.
- Treating the kidney figure as exact. If the builder's papers give a volume, type that into the volume field on the dosing screen instead.
- Measuring once. Check the pool a second time, because a 10 cm error in average depth on a 8 m by 4 m pool is 3.2 m³.