How to Calculate Pool Volume in Litres, Gallons and m³

Calculate your pool's volume in litres, gallons or m³ for any shape, including the sloped-floor formula that avoids a 20-30 % overestimate.

Why pool volume in litres matters

Knowing your pool volume in litres is the single most useful number for day-to-day pool management. Every chemical dose on the label is written per 1,000 or 10,000 litres. Every heat pump datasheet is sized for a water volume range. Every filtration cycle is calculated as a fraction of the pool volume moved per hour. Get this number wrong by 20 % and you will either underdose (cloudy water, algae) or overdose (skin irritation, equipment corrosion, wasted product).

This guide gives you the exact formulas, a quick-reference conversion table and the practical tips that keep you out of the two most common mistakes: using average depth on a sloped bottom and confusing radius with diameter.

Common Pool Sizes: Volume in Litres and Gallons

Imperial sizes, 5 ft average depth

Metric sizes, 1.5 m average depth

These figures assume a constant average depth. Many pools have a flat shallow section, a slope and a flat deep end, and when the shallow section is the longer one the real volume is lower than the simple average of the two depths suggests. An 8 × 4 m pool that is 1.0 m deep for half its length, slopes over the next quarter and is 2.0 m deep in the last quarter holds 44,000 litres, not the 48,000 litres the 1.5 m average gives: about 8 % less. Use our pool volume calculator with your actual bottom profile for an accurate figure.

How many litres is a 16x32 pool?

A 16 × 32 ft pool with an average depth of 5 ft holds about 72,500 litres (19,150 US gallons). The exact figure depends on the bottom profile: if the shallow end is longer than the deep end, the real volume is lower than that average suggests.

How many gallons is a 40x20 pool?

A 40 × 20 ft pool holds about 29,900 US gallons (113,300 litres) at an average depth of 5 ft. Each extra foot of average depth adds roughly 6,000 gallons.

How many litres is a 15x30 pool?

A 15 × 30 ft pool holds about 63,700 litres (16,800 US gallons) at an average depth of 5 ft. At a 4 ft average depth it is about 51,000 litres.

The conversion that never changes: m³ to litres

One cubic metre of water always equals exactly one thousand litres:

1 m³ = 1,000 L

Every formula below returns the volume in m³. To get litres, multiply by 1,000. To convert to US gallons multiply by 264.17; to UK gallons, multiply by 219.97.

Formula per pool shape

Rectangular pool with flat bottom

V (m³) = length × width × depth

Example: an 8 × 4 m pool with 1.5 m depth:

V = 8 × 4 × 1.5 = 48 m³ = 48,000 L

Rectangular pool with sloped bottom

Use the average depth, not the deep-end or shallow-end depth alone:

V (m³) = length × width × (depth_shallow + depth_deep) / 2

Example: an 8 × 4 m pool with 1.2 m in the shallow end and 1.8 m in the deep end:

V = 8 × 4 × (1.2 + 1.8) / 2 = 8 × 4 × 1.5 = 48 m³ = 48,000 L

This works when the slope is linear (a single ramp). For pools with a hopper bottom (flat shallow, sudden drop, flat deep), split the pool into two rectangles and add the volumes.

Round pool

V (m³) = π × r² × h

Where r is the radius (half the diameter) and h is the water depth. Example: a 4.57 m diameter, 1.07 m water depth Intex frame pool:

V = 3.1416 × 2.285² × 1.07 = 17.55 m³ = 17,550 L

If you prefer to work directly with diameter D:

V (m³) ≈ 0.7854 × D² × h

Oval pool

V (m³) = length × width × depth × 0.893

Where length and width are the outer measurements of the oval and 0.893 is a shape factor that accounts for the pool being an oval, not a rectangle. Example: a 6.10 × 3.66 m Bestway oval pool with 1.22 m water depth:

V = 6.10 × 3.66 × 1.22 × 0.893 = 24.30 m³ = 24,300 L

Kidney or free-form pool

Approximate as: V (m³) = length × width × avg_depth × 0.85

The 0.85 factor absorbs the concavity of the shape. For precision, split the pool into two or three rectangles and add.

Quick reference table: common pool sizes

Volume in litres for the most frequent residential pool footprints, at 1.5 m average water depth:

Common mistakes when calculating pool volume

1. Using pool wall height instead of water depth. Pools are filled to 90 % of wall height for splash safety. Always measure the actual water level.
2. Confusing radius with diameter on round pools. The radius is half the diameter. Using the diameter as radius returns 4× the real volume.
3. Ignoring the sloped bottom. Using deep-end depth on a sloped pool overestimates volume by 20-30 %.
4. Rounding metric measurements to the wrong precision. A 5-cm error on a 5 m pool creates a 1 % volume error, which is acceptable; a 5-cm error on a 3 m pool creates a 1.7 % error.
5. Using the manufacturer's rated volume as gospel. Above-ground pool boxes state volume at 80 % or 90 % fill. Real usable water can differ by 10-15 %.

Application 1: chemical dosing

All pool chemicals are dosed per 1,000 or 10,000 litres of water. Quick reference for a typical 40,000 L pool (40 m³):

• Shock chlorination (10 g/m³ free chlorine): 400 g of granular tri-chlor or 1.2-1.5 L of 10 % liquid chlorine.
• Salt initial charge for salt chlorinator (4 g/L target): 160 kg of pool salt.
• pH decrease with muriatic acid (33 %): about 100 mL to drop pH by 0.1 units.
• Algaecide: typical dose 100 mL per 40,000 L per week.

A 20 % volume error on this pool means dosing 40 g of chlorine short or long — enough to leave water cloudy or cause skin irritation for swimmers.

Application 2: pump and filter sizing

Rule of thumb: your pump flow rate in m³/h should move the total pool volume once every 4 to 6 hours of operation. For a 48 m³ pool at 6 h/cycle:

Required flow rate = 48 / 6 = 8 m³/h

This determines the pump model and the filter size (a sand filter must handle the flow at <50 m³/h per m² of filtering surface). Undersizing means longer daily filtration to compensate; oversizing wastes electricity and can turbulently move debris past the skimmer.

Application 3: heater and heat pump dimensioning

Raising 1 m³ of pool water by 1 °C takes about 1.16 kWh of net heat. For a 40 m³ pool with a 5 °C temperature rise target (18 → 23 °C):

Net heat needed = 40 × 5 × 1.16 ≈ 232 kWh

A heat pump with 8 kW of thermal output would take 29 hours of continuous operation to reach the target, before accounting for losses through the water surface (typically 30-50 % additional in unheated exposure). Wrong volume, wrong heat pump.

Do the calculation online in 10 seconds

Save yourself the arithmetic. At /tools/pool-volume-calculator you can enter your pool dimensions and shape and receive:

• Volume in m³ and litres.
• Equivalent in US and UK gallons.
• Suggested chemical doses for shock chlorination and pH adjustment.
• Recommended pump flow range.

If you want to go further and get an estimated EN 17645 environmental class for your pool along with a unique PoolLex ID, generate your free Technical Sheet at /ficha-tecnica.

PoolLex.io turns your pool volume and equipment data into a complete technical diagnostic: chemical dosing, running-cost estimate and A-F environmental class per EN 17645:2023. Start free at /ficha-tecnica.