The formula
volume = surface area × average depth · litres = m³ × 1,000
Where it comes from
Where the floor slopes, the depth that counts is the average between the shallow and deep ends. The volume in cubic metres converts to litres by multiplying by a thousand, because a cubic metre is exactly a thousand litres.
How to work it out by hand
- Work out the area of the water surface
- Find the average depth between the shallow and deep ends
- Multiply the area by the average depth
- Multiply by 1,000 for litres
What is worth knowing
The pump should turn over the whole volume in four to six hours, so its flow rate comes from dividing the cubic metres by five. Shock chlorination at the start of the season uses around 10 grams per cubic metre; daily maintenance, around 2. Those doses are indicative: what governs is the measured free chlorine level, between 0.5 and 2 parts per million.