Pool Volume Calculator — UK
Metric by default: metres in, litres out. Salt targets 2700–3400 mg/L.
Pool volume formulas (litres and gallons)
- • Rectangle: Length × Width × Avg depth × 1,000 = litres (× 7.5 = US gallons)
- • Round: π × (Diameter ÷ 2)² × Depth × 1,000 = litres
- • Oval: π × (Length ÷ 2) × (Width ÷ 2) × Depth × 1,000 = litres
- • Kidney: 0.45 × (Wide lobe + Narrow waist) × Length × Depth × 1,000 (±10% estimate)
Average depth = (shallow end + deep end) ÷ 2, measured at the waterline. 1 m³ = 1,000 L · 1 US gallon = 3.785 L · 1 UK gallon = 4.546 L.
Common UK pool sizes
| Type | Dimensions | Approx. volume |
|---|---|---|
| Round above-ground | 12 ft Ø × 4 ft water | ~3,400 gal (~12,900 L) |
| Round above-ground | 15 ft Ø × 4 ft water | ~5,300 gal (~20,100 L) |
| Round above-ground | 18 ft Ø × 4 ft water | ~7,600 gal (~28,800 L) |
| Round above-ground | 24 ft Ø × 4 ft water | ~13,500 gal (~51,100 L) |
| Oval above-ground | 15 × 30 ft × 4 ft water | ~10,600 gal (~40,100 L) |
| Rectangle in-ground | 16 × 32 ft × 5 ft avg | ~19,200 gal (~72,700 L) |
Pool volume FAQs
How do I calculate pool volume in litres?
Measure length, width and average depth in metres, multiply the three, then multiply by 1,000. An 8 × 4 m pool at 1.5 m average depth holds 48,000 litres. Round pools use π × radius² × depth × 1,000.
What is the difference between US and UK gallons?
1 US gallon = 3.785 litres; 1 UK (imperial) gallon = 4.546 litres. A pool holding 10,000 US gallons holds about 37,850 litres but only about 8,326 UK gallons. Check which gallon your chemical label uses — when in doubt, dose by litres.
How much water does an above-ground round pool hold?
Use π × radius² × water depth (not wall height — water sits ~6" below the top rail). An 18 ft round pool at 4 ft of water holds about 7,600 gallons (≈28,800 litres).
Should I use average depth or deep-end depth?
Always average: (shallow + deep) ÷ 2, measured at the waterline. Using deep-end depth alone can overdose every chemical by up to 40%.
Why does pool volume matter for chemicals?
Every dose is per unit of water — chlorine granules at 1–3 mg/L, salt at 2700–3400 mg/L. Wrong volume means algae from under-dosing or damage and waste from over-dosing. Calculate volume first, then dose with our chemical, chlorine and salt calculators.