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Pool Calculator for the UK
Volume in litres, chemicals in grams, heating in kW. Accurate, fast, and free for UK pool owners.
Pool Volume Calculator (Litres)
Enter metres — get litres + gallons. 1 m³ = 1,000 L.
How to calculate pool volume in litres
To calculate pool volume in litres, measure length, width and average depth in metres, multiply the three together, then multiply by 1,000. An 8 × 4 metre pool at 1.5 m average depth holds 8 × 4 × 1.5 × 1,000 = 48,000 litres. Average depth means (shallow end + deep end) ÷ 2. Always measure the water itself, not the wall height: above-ground walls run 48"–52" but water sits about 6 inches lower, and every chemical dose follows from the water you actually treat.
US gallons, UK gallons and litres — which one?
This is the question that trips up UK pool owners: 1 US gallon = 3.785 litres, but 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. Always check which gallon your chemical label uses before dosing; when labels disagree, dose by litres. Our pool volume calculator shows US gallons and litres side by side, and 1 cubic metre equals exactly 1,000 litres.
Above-ground round and oval volumes
Most UK garden pools are above-ground round or oval models with flat bottoms — no averaging needed, just water depth. A round pool volume calculator uses π × radius² × depth: an 18 ft round pool at 4 ft of water holds about 7,600 US gallons (≈28,800 litres). Oval pools use π × (length ÷ 2) × (width ÷ 2) × depth: a 15 × 30 ft oval at 4 ft holds about 10,600 gallons (≈40,100 litres). Kidney and freeform pools use the 0.45 industry estimate (±10%) — add two-thirds of any dose, retest, then top up.
Why pool volume matters for chemicals
Every dose is per unit of water: chlorine granules at 1–3 mg/L with regular shock dosing, salt systems at 2700–3400 mg/L, and pH Plus/Minus to hold pH at 7.2–7.6, checked with test strips for alkalinity and chlorine. Dose off the wrong volume and you under-dose into algae or over-dose into bleached liners and wasted product. Calculate volume first in our pool chemical calculator, then carry the number into chlorine and salt pool calculator — they pick it up automatically.
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) |
Olympic swimming pool volume in litres
An Olympic swimming pool holds 2,500 cubic metres of water: 2,500,000 litres, about 660,000 US gallons. A typical 19,200-gallon backyard pool is roughly one-thirty-fourth of that — a handy sanity check that your own result sits in a believable range.
Cost to fill a pool in the UK
Metered water is billed per cubic metre — find the £/m³ figure on your bill and multiply by your pool's m³. A 73 m³ pool at £2/m³ is roughly £146, plus top-ups through summer as splash-out and evaporation bite. A cover cuts both, which is why our pool cost calculator factors it into every estimate.
UK targets (mg/L = ppm)
Same numbers as US ppm — label reads mg/L for trust. Salt 2700–3400 mg/L.
Chemical Calculator
Exact doses in grams & litres for balanced water
Chlorine Calculator
Daily chlorine + shock in metric units
Salt Water Calculator
Salt in kg for 2700–3400 mg/L systems
LSI Balance Calculator
Corrosive, balanced or scaling? One number.
Heating Calculator
Heating time + energy cost in kWh
Cost Calculator
Fill, heating and maintenance in GBP
UK salt: 2700–3400 mg/L
Same range as US pools — default 3200 mg/L, 20 kg bags. Never above 4000 mg/L (4 g/L).