Garden & outdoor
How many litres of water does your pool hold?
Free pool water calculator: litres and m³ for rectangular or round pools, plus filter pump flow and maintenance chlorine dose.
Quick answer
Every pool maintenance decision starts from one number you can’t read anywhere on the pool: how many litres it holds. Chlorine dose, pH correction, filter size, even how long the pump should run — everything is dosed per cubic metre. For a rectangular pool it’s length × width × average depth, where average depth is the midpoint between the shallow and deep ends; for a round pool, radius squared × π × depth.
Water volume
34,300 L (34.3 m³)
- Recommended pump flow
- 8.6 m³/h
- Weekly chlorine (slow tablets)
- ~400 g (200 g tablets)
Opening or treating the pool? Chlorine dose calculator
Average depth = (shallow end + deep end) ÷ 2. The pump should turn over the full volume in about 4 hours, running 8 h a day in season. Maintenance chlorine is roughly 1 slow-release 200 g tablet per 20-25 m³ per week, keeping free chlorine at 1-1.5 ppm and pH between 7.2 and 7.6 — always verify with a test kit.
How it works
The calculator adds the two numbers that follow directly from volume. Filter pump flow: the whole volume should pass through the filter in about 4 hours, so a 30 m³ pool wants a pump around 7.5 m³/h, running roughly 8 hours a day in season. And maintenance chlorine: about one 200 g slow-release tablet per 20-25 m³ per week, targeting 1-1.5 ppm of free chlorine with pH between 7.2 and 7.6 — outside that pH window, chlorine loses most of its power no matter how much you add.
If the pool is not a rectangle, there is a way to get the volume without any geometry at all. Read the water meter, fill the pool from the mains, and read it again: the difference is the exact volume, with no formula and no error from a kidney shape or a sloping floor. Where the pool is already full, do it on the top ten centimetres — top up from empty-to-line and multiply. Failing a meter, a garden hose delivers roughly ten to fifteen litres a minute, which you can measure once with a bucket and a watch, then time the fill. It is the only method that is exact on an irregular pool. Once you have the litres every other pool decision follows from them: the chlorine dose is grams per cubic metre, so this number is the input the rest of the season needs.
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Frequently asked questions
How many liters is a typical above-ground pool?+
Common sizes: a round 3.6 m pool with 1.2 m of water holds about 12,000 L; a 4.5 m round about 19,000 L; a rectangular 7.3 × 3.7 m frame pool around 30,000 L. In-ground family pools typically run 40,000-80,000 L. Use the exact water level, not the wall height — pools fill to 10-15 cm below the rim.
How much chlorine do I put in per week?+
For maintenance, roughly one 200 g slow-release trichlor tablet per 20-25 m³ per week, placed in a floating dispenser or skimmer basket. The real target is 1-1.5 ppm of free chlorine measured with test strips, and consumption doubles in heatwaves and heavy use. Shock treatment (after storms, green water or many bathers) is a separate, much higher dose of fast-dissolving chlorine.
How long should the pool pump run each day?+
The standard is one to two full turnovers a day: with a pump sized for a 4-hour turnover, that means about 8 hours daily in season, ideally during daylight when chlorine demand peaks. In spring and autumn 4-6 hours suffice. Running it too little shows up fast as cloudy water — filtration, not chlorine, does most of the clarity work.
My pool water is green — what do I do?+
Green means algae, and the fix is always the same sequence: brush walls and floor, correct pH to 7.2, shock-chlorinate at 3-5× the normal dose (fast-dissolving granules, dosed by your volume — this is where knowing your litres matters), then run the pump continuously for 24-48 hours and clean the filter afterwards. If it’s green again within days, test cyanuric acid: over-stabilized water stops chlorine working.
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