Putting volume to work
Pool volume for filling, salt and filtration
Four practical calculations come from the same figure, provided units stay consistent and manufacturer guidance is followed.
Start with net volume, measure installation-specific inputs and treat each result as an estimate to verify.
Filling time
Convert volume to litres and divide by the actual hose flow in litres per minute. For 40,000 L at 20 L/min, allow about 2,000 minutes, or 33 h 20, before flow variations.
Water cost
Multiply cubic metres by the full variable tariff shown on the bill. Check whether wastewater, tax or local restrictions apply. Fixed subscription charges are normally separate.
Salt to add
For a salt system, a 1 g/L salinity gap numerically equals 1 kg per m³. A 40 m³ pool with a 1 g/L gap therefore needs 40 kg in theory.
- Confirm the target in the salt-system manual.
- Allow for test accuracy.
- Add gradually and retest before completing the dose.
Theoretical filtration flow
Divide volume by the chosen turnover time. A 48 m³ pool over 6 hours corresponds to 8 m³/h in theory.
Actual selection also depends on head loss, filter and pipework. Seek professional validation when needed.
Safety rules
Never transfer a dose without reading the label and testing the water. Wear specified protective equipment, never mix products and follow local rules. The CDC recommends trained chemical handlers for public pools.
FAQ
Gross or net volume?
Usually use net water volume because it deducts submerged solid features.
Is calculated flow enough to choose a pump?
No. Filter, pipework, head loss and manufacturer guidance also matter.
Should all calculated salt be added at once?
Add gradually and retest to allow for measurement uncertainty and salt already present.
Sources and limitations
Start with net volume, measure installation-specific inputs and treat each result as an estimate to verify.