Pool Volume Calculator
Find out exactly how many gallons or litres your pool holds. Works for every pool shape in seconds.
Pick the shape that best matches your pool. Above-ground round pools use the diameter x wall-height-in-inches format common on boxes and listings.
Why You Need to Know Your Pool Volume
Your pool volume in gallons is the foundation of every maintenance decision you make. Without it, you are guessing on chemical doses, pump sizing, salt amounts, and fill costs. Every pool chemical product is dosed per 10,000 gallons – chlorine, shock, algaecide, salt, pH adjusters, alkalinity increaser. Get the volume wrong and every dose is off by the same percentage.
Pool Volume Formulas for Every Shape
Rectangular Pool
Gallons = Length x Width x Average Depth x 7.48
Example: 32 ft x 16 ft, shallow end 3.5 ft, deep end 6 ft. Average depth = (3.5 + 6) / 2 = 4.75 ft. Volume = 32 x 16 x 4.75 x 7.48 = 18,188 gallons.
Round / Circular Pool
Gallons = Pi x Radius x Radius x Depth x 7.48
Example: 18 ft diameter, 4 ft deep. Radius = 9 ft. Volume = 3.14159 x 9 x 9 x 4 x 7.48 = 7,637 gallons.
Oval Pool
Gallons = Length x Width x 0.785 x Average Depth x 7.48
Example: 30 x 15 ft oval, 5 ft deep. Volume = 30 x 15 x 0.785 x 5 x 7.48 = 13,196 gallons.
Kidney Pool
Gallons = 0.45 x (Width A + Width B) x Length x Depth x 7.48
Width A is the wider end, Width B is the narrower end, Length is the longest dimension. Example: A = 16 ft, B = 10 ft, Length = 32 ft, depth = 5 ft. Volume = 0.45 x 26 x 32 x 5 x 7.48 = 13,951 gallons.
L-Shape Pool
Divide into two rectangles. Calculate each separately and add them. Example: Section A = 25 x 15 ft, Section B = 12 x 10 ft, depth = 5 ft. Volume = (375 + 120) x 5 x 7.48 = 18,513 gallons.
Above-Ground Round Pool (Diameter x Inches Format)
Above-ground pool sizes on the box are listed as diameter in feet x wall height in inches. An 18×48 pool is 18 ft diameter with a 48-inch wall. Actual usable water depth is 6 inches less than wall height.
Water depth (ft) = (Wall height in inches – 6) / 12
Gallons = Pi x (Diameter/2)^2 x Water depth x 7.48
Example: 18×48 pool. Water depth = (48 – 6) / 12 = 3.5 ft. Gallons = 3.14159 x 9 x 9 x 3.5 x 7.48 = 6,682 gallons.
Freeform and Irregular Pools
Gallons = Longest Length x Widest Width x Average Depth x 0.85 x 7.48
The 0.85 factor accounts for the irregular edges. Result is an estimate within 5 to 10% for most freeform shapes. For better accuracy, break the pool into recognizable sections and calculate each separately.
Common Pool Sizes and Gallon Chart
| Pool size | Shape | Avg depth | Gallons | Litres |
|---|---|---|---|---|
| 12 x 24 ft | Rectangle inground | 4.5 ft | 9,720 | 36,800 |
| 14 x 28 ft | Rectangle inground | 5 ft | 14,700 | 55,600 |
| 16 x 32 ft | Rectangle inground | 5 ft | 19,200 | 72,700 |
| 18 x 36 ft | Rectangle inground | 5 ft | 24,200 | 91,600 |
| 18 x 36 ft | Rectangle inground | 5.5 ft | 26,600 | 100,700 |
| 20 x 40 ft | Rectangle inground | 5 ft | 29,800 | 112,800 |
| 20 x 40 ft | Rectangle inground | 5.5 ft | 32,800 | 124,200 |
| 15 ft dia (15×48) | Round above-ground | 3.5 ft | 4,650 | 17,600 |
| 18 ft dia (18×48) | Round above-ground | 3.5 ft | 6,680 | 25,300 |
| 18 ft dia (18×52) | Round above-ground | 3.83 ft | 7,300 | 27,600 |
| 21 ft dia (21×52) | Round above-ground | 3.83 ft | 9,900 | 37,500 |
| 24 ft dia (24×52) | Round above-ground | 3.83 ft | 13,000 | 49,200 |
| 27 ft dia (27×52) | Round above-ground | 3.83 ft | 16,500 | 62,500 |
| 30 ft dia (30×52) | Round above-ground | 3.83 ft | 20,300 | 76,800 |
| 30 x 15 ft | Oval inground | 5 ft | 13,200 | 50,000 |
| Kidney 16+10 wide, 32 ft | Kidney inground | 5 ft | 14,000 | 53,000 |
Above-Ground Pool Volumes: The Diameter x Inches Format
Every above-ground pool sold in the US lists size as diameter in feet x wall height in inches. This trips up most pool owners who assume both numbers are in feet. An 18×48 pool is 18 feet diameter with a 48-inch (4 ft) wall. An 18×52 pool has the same footprint but a 52-inch (4.33 ft) wall and holds about 9% more water.
| Pool model size | Diameter | Wall height | Water depth | Gallons |
|---|---|---|---|---|
| 15×48 | 15 ft | 48 in | 3.5 ft | 4,650 |
| 18×48 | 18 ft | 48 in | 3.5 ft | 6,680 |
| 18×52 | 18 ft | 52 in | 3.83 ft | 7,300 |
| 21×52 | 21 ft | 52 in | 3.83 ft | 9,900 |
| 22×52 | 22 ft | 52 in | 3.83 ft | 10,900 |
| 24×52 | 24 ft | 52 in | 3.83 ft | 13,000 |
| 24×54 | 24 ft | 54 in | 4.0 ft | 13,600 |
| 27×52 | 27 ft | 52 in | 3.83 ft | 16,500 |
| 27×54 | 27 ft | 54 in | 4.0 ft | 17,200 |
| 30×52 | 30 ft | 52 in | 3.83 ft | 20,300 |
How Big Is a 10,000 / 15,000 / 20,000 / 25,000 / 30,000 Gallon Pool?
If you know your pool volume in gallons and want to know what size pool that is, here is the reverse lookup for standard rectangular inground pools at 5 ft average depth:
| Volume | Approximate size at 5 ft depth | Litres |
|---|---|---|
| 10,000 gallons | 12 x 22 ft rectangle, or 18 ft round above-ground | 37,900 |
| 15,000 gallons | 14 x 28 ft rectangle | 56,800 |
| 20,000 gallons | 16 x 33 ft rectangle | 75,700 |
| 25,000 gallons | 18 x 34 ft rectangle | 94,600 |
| 30,000 gallons | 20 x 40 ft rectangle at 5 ft depth | 113,600 |
| 50,000 gallons | Large custom pool or 25 metre lap pool | 189,300 |
How Pool Volume Affects Chemical Dosing
Every pool chemical is dosed per 10,000 gallons. Divide your pool volume by 10,000, then multiply by the dose below to get your exact amount. For daily sanitizer management, our swimming pool chlorine calculator takes the guesswork out of chlorine dosing for your specific pool volume.
| Chemical | Dose per 10,000 gallons | Purpose |
|---|---|---|
| Liquid chlorine (12.5%) | 20 fl oz weekly | Primary sanitizer |
| Trichlor tablets (3-inch) | 1 tablet per week | Ongoing sanitization |
| Shock (calcium hypochlorite) | 1 lb per treatment | Oxidize contaminants |
| CYA stabilizer – to reach 40 ppm | 13 oz | Protect chlorine from UV |
| Salt – from zero to 3,200 ppm | 267 lbs (7 x 40 lb bags) | Saltwater chlorination |
| Alkalinity increaser – raise 10 ppm | 1.5 lbs | Stabilize pH |
| pH increaser (soda ash) – raise 0.2 | 6 oz | Correct low pH |
| pH decreaser (muriatic acid) – lower 0.2 | 6 fl oz | Correct high pH |
| Calcium hardness increaser – raise 10 ppm | 1.25 lbs | Prevent corrosion |
If you operate a saltwater chlorine generator, getting your salinity right from the start is critical. The salt calculator for pools tells you exactly how many pounds or bags of pool salt to add based on your pool volume and current salt reading, so your salt cell runs at peak efficiency.
How to Measure Average Pool Depth
Most inground pools have a shallow end and a deep end. The simple average works for pools with flat shelves at each end:
Simple average = (Shallow end + Deep end) / 2
For pools with a long gradual slope, this weighted formula is more accurate:
Weighted average = (Shallow end x 0.333) + (Deep end x 0.667)
How to Size a Pool Pump Using Volume
Your pump must turn over the full pool volume at least twice every 24 hours. One turnover cycle is calculated over 8 hours of run time.
Minimum GPM = Pool volume / 480
For a 20,000-gallon pool: 20,000 / 480 = 41.7 GPM. Choose a pump rated for at least 42 GPM at your system head pressure. Variable speed pumps achieve the required turnovers at 70 to 80% less electricity than single-speed pumps by running at low speed for longer periods. For help selecting the right pump size for your specific pool, use our pool pump sizing calculator.
Your pool volume is also the key input for sizing a pool heater correctly. Our pool heater BTU calculator uses your gallonage to recommend the right heater size for efficient, fast heating without wasting energy on an oversized unit.
How Long Does It Take to Fill a Pool?
| Pool volume | 1 hose (500 GPH) | 2 hoses (1,000 GPH) | Water truck (3,000 GPH) |
|---|---|---|---|
| 7,500 gal (18×48 above-ground) | 15 hrs | 7.5 hrs | 2.5 hrs |
| 10,000 gallons | 20 hrs | 10 hrs | 3.3 hrs |
| 15,000 gallons | 30 hrs | 15 hrs | 5 hrs |
| 20,000 gallons | 40 hrs | 20 hrs | 6.7 hrs |
| 25,000 gallons | 50 hrs | 25 hrs | 8.3 hrs |
| 30,000 gallons | 60 hrs | 30 hrs | 10 hrs |
For a new concrete pool fill, run the hose continuously without interruption. Stopping and restarting on fresh plaster leaves hard water lines that are very difficult to remove. For a customized fill time estimate based on your exact pool volume and water source flow rate, try our pool fill time calculator.
Hot Tub and Spa Volume
Hot tubs and pool spas require precise chemistry because the small volume and high temperature amplify the effect of every chemical added. Small 2-person hot tubs hold 300 to 500 gallons. Standard 4-person hot tubs hold 600 to 900 gallons. Large 6 to 8 person hot tubs hold 900 to 1,500 gallons. Attached pool spas are typically 600 to 1,200 gallons. Use the calculator above with the Hot tub / Spa shape option for your exact volume.
Frequently Asked Questions
How many gallons are in a standard pool?
A standard 16 x 32 ft inground pool at 5 ft average depth holds about 19,200 gallons or 72,700 litres. A 14 x 28 ft pool at 5 ft depth holds about 14,700 gallons. An 18 ft round above-ground pool with a 48-inch wall holds about 6,680 gallons.
How many gallons is an 18 x 36 pool?
An 18 x 36 ft rectangular inground pool at 5 ft average depth holds approximately 24,200 gallons or 91,600 litres. At 5.5 ft average depth it holds about 26,600 gallons. This is one of the most common residential inground pool sizes in the US.
How many gallons is a 20 x 40 pool?
A 20 x 40 ft rectangular pool at 5 ft average depth holds approximately 29,800 gallons. At 5.5 ft depth it holds about 32,800 gallons. At 6 ft average depth the volume reaches 35,800 gallons.
How many gallons is an 18×48 above-ground pool?
An 18×48 above-ground pool (18 ft diameter, 48-inch wall) holds approximately 6,680 gallons at standard fill depth of 42 inches. Never fill to the full wall height – usable water depth is wall height minus 6 inches.
How many gallons is an 18×52 above-ground pool?
An 18×52 above-ground pool (18 ft diameter, 52-inch wall) holds approximately 7,300 gallons at standard fill level of 46 inches water depth.
How many gallons is a 21 ft round pool?
A 21 ft round above-ground pool with a 52-inch wall holds approximately 9,900 gallons. With a 48-inch wall it holds about 9,100 gallons. The 21×52 is one of the most popular above-ground pool sizes sold in the US.
How many gallons is a 24 ft round pool?
A 24 ft round above-ground pool with a 52-inch wall holds approximately 13,000 gallons. A 24×48 model holds about 11,900 gallons. For an inground 24 ft round pool at 5 ft depth the volume is approximately 16,900 gallons.
How many gallons is a 27 ft round pool?
A 27 ft round above-ground pool with a 52-inch wall holds approximately 16,500 gallons. With a 54-inch wall it holds about 17,200 gallons. This is a large above-ground pool that requires the same equipment and chemical care as a standard inground pool.
How many gallons in a 16 x 32 pool?
A 16 x 32 ft rectangular pool at 5 ft average depth holds approximately 19,200 gallons or 72,700 litres. This is the most common residential inground pool size in the United States. At 4.5 ft depth it holds about 17,200 gallons.
How many litres are in a swimming pool?
A standard residential inground pool holds between 55,000 and 125,000 litres depending on size. A 16 x 32 ft pool at 5 ft depth holds 72,700 litres. Multiply US gallons by 3.785 to convert to litres.
How do I calculate my pool volume without a calculator?
For rectangular pools: length x width x average depth x 7.48. For round pools: 3.14 x (diameter/2)^2 x depth x 7.48. For above-ground round pools: 3.14 x (diameter/2)^2 x ((wall height inches – 6) / 12) x 7.48. All results are in US gallons.
Why do some pool formulas use 7.5 and others 7.48?
One cubic foot of water contains exactly 7.48052 US gallons. Many pool guides round to 7.5 for easier mental math. The difference is less than 0.3% and has no meaningful impact on chemical dosing decisions.
Does pool volume include water in the pipes and filter?
The volume calculated here covers the pool basin only. Water in pipes, the filter tank, and the heater adds roughly 50 to 150 gallons depending on your equipment. For chemical dosing this difference is within normal measurement error and is typically ignored.
Tips for Accurate Pool Measurements
- Measure at the water surface, not the shell edge. The shell is always slightly larger than the water area.
- For above-ground round pools, measure the inside diameter. The wall takes up 2 to 4 inches on each side.
- Measure depth at normal operating level – water at the midpoint of the skimmer opening.
- Check your original pool documents. Volume is often listed on pool construction permits, builder invoices, and salt cell controller settings.
- Double-check by measuring twice from different starting points to catch tape measure errors.
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