Pool Volume Calculator
Find out exactly how many gallons your pool holds. Works for every pool shape, in seconds.
Why You Need to Know Your Pool Volume
Your pool volume in gallons is the foundation for almost every pool maintenance decision you make. Without it, you are guessing on chemical doses, pump sizing, salt amounts, and fill costs. Get it wrong and you either under-treat your pool (leading to algae and bacteria) or over-treat it (wasting money and potentially irritating swimmers).
The three most common reasons pool owners need their volume:
- Adding chemicals. Every chemical dose is calculated per 10,000 gallons. Chlorine, shock, algaecide, salt, pH increaser, pH decreaser — all of them.
- Sizing a pump or filter. Your pump needs to turn over your pool’s full volume at least twice every 24 hours. Too small a pump and the water doesn’t circulate properly. Too large and you waste electricity.
- Calculating fill cost. Knowing your volume lets you estimate exactly how much a refill will cost before you open the tap.
Pool Volume Formulas by Shape
Every pool shape uses a different formula. Here is each one written out simply, with worked examples.
Rectangular Pool Formula
Volume = Length x Width x Average Depth x 7.48
The 7.48 converts cubic feet to US gallons (there are exactly 7.48052 gallons in one cubic foot).
Example: A pool that is 32 ft long, 16 ft wide, with a shallow end of 3.5 ft and deep end of 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 Formula
Volume = 3.14159 x Radius x Radius x Average Depth x 7.48
Radius is half the diameter. Measure the pool at its widest point across, then divide by 2.
Example: An 18 ft diameter round pool, 4 ft deep:
- Radius = 18 / 2 = 9 ft
- Volume = 3.14159 x 9 x 9 x 4 x 7.48 = 7,637 gallons
Oval Pool Formula
Volume = Length x Width x 0.785 x Average Depth x 7.48
The 0.785 is pi divided by 4, which accounts for the oval shape being roughly 78.5% of the area of a rectangle with the same dimensions.
Example: A 30 ft x 15 ft oval, 5 ft average depth:
- Volume = 30 x 15 x 0.785 x 5 x 7.48 = 13,196 gallons
Kidney Pool Formula
Volume = 0.45 x (Width A + Width B) x Length x Average Depth x 7.48
Width A is the widest end of the kidney shape, Width B is the narrowest end, and Length is the longest dimension.
Example: Width A = 16 ft, Width B = 10 ft, Length = 32 ft, average depth = 5 ft:
- Volume = 0.45 x (16 + 10) x 32 x 5 x 7.48 = 13,951 gallons
L-Shape Pool Formula
Divide the L-shape into two rectangles. Calculate each section separately, then add them together.
Volume = (Section A: L x W + Section B: L x W) x Average Depth x 7.48
Example: Section A is 25 x 15 ft, Section B is 12 x 10 ft, average depth 5 ft:
- Area = (25 x 15) + (12 x 10) = 375 + 120 = 495 sq ft
- Volume = 495 x 5 x 7.48 = 18,513 gallons
Freeform / Irregular Pool
There is no exact formula for freeform pools. The best approach is to measure the longest length and widest width, calculate as if it were a rectangle, then multiply by 0.85 to account for the curves and missing corners.
Volume = Length x Width x Average Depth x 0.85 x 7.48
This gives a reasonable estimate for most freeform shapes. For a more precise figure, break the pool into recognisable sections (rectangles, half-circles) and calculate each separately.
How to Measure Average Pool Depth
Most pools are not the same depth from end to end. They have a shallow end where you can stand and a deep end for diving or laps. To get the right volume, you need the average depth, not just one measurement.
The formula is simple:
Average depth = (Shallow end depth + Deep end depth) / 2
For a pool with a 3.5 ft shallow end and a 6 ft deep end, the average depth is (3.5 + 6) / 2 = 4.75 ft.
For pools with a gradual slope from shallow to deep (rather than a flat shelf at each end), use this more accurate formula:
Average depth = Shallow end depth x 0.333 + Deep end depth x 0.667
This weights the deeper end more heavily, which gives a more accurate average for pools with a long gradual slope.
Common Pool Sizes and Volumes
| Pool Size | Shape | Avg Depth | Volume (gallons) |
|---|---|---|---|
| 12 x 24 ft | Rectangle | 4.5 ft | ~9,700 gal |
| 14 x 28 ft | Rectangle | 5 ft | ~14,700 gal |
| 16 x 32 ft | Rectangle | 5 ft | ~19,200 gal |
| 18 x 36 ft | Rectangle | 5.5 ft | ~26,600 gal |
| 20 x 40 ft | Rectangle | 5.5 ft | ~32,800 gal |
| 15 ft diameter | Round (above ground) | 4 ft | ~5,300 gal |
| 18 ft diameter | Round (above ground) | 4 ft | ~7,600 gal |
| 24 ft diameter | Round (above ground) | 4.5 ft | ~15,200 gal |
| 30 x 15 ft | Oval | 5 ft | ~13,200 gal |
| Kidney (16+10 wide, 32 ft long) | Kidney | 5 ft | ~14,000 gal |
How Pool Volume Affects Chemical Dosing
Every pool chemical product gives dosing instructions per 10,000 gallons. This makes it easy to scale once you know your volume.
| Chemical | Dose per 10,000 gallons | Purpose |
|---|---|---|
| Liquid chlorine (12.5%) | 20 fl oz weekly | Sanitise the water |
| Chlorine tablets (3-inch) | 1 tablet weekly | Ongoing sanitisation |
| Shock (calcium hypochlorite) | 1 lb per treatment | Oxidise contaminants |
| Pool salt (to reach 3,200 ppm) | ~267 lbs (7 x 40lb bags) | Saltwater chlorination |
| Algaecide | 4 fl oz weekly | Prevent algae growth |
| pH increaser (soda ash) | 6 oz to raise 0.2 pH | Balance water pH |
| pH decreaser (muriatic acid) | 6 fl oz to lower 0.2 pH | Balance water pH |
| Alkalinity increaser | 1.5 lbs to raise 10 ppm | Stabilise pH |
How to Size a Pool Pump Using Volume
Your pump needs to circulate the entire pool volume at least twice in 24 hours. This is called the turnover rate. Most pool professionals recommend 2 to 3 turnovers per day.
To find the minimum flow rate your pump needs:
Minimum GPM = Pool volume in gallons / 480
The 480 is the number of minutes in 8 hours (a single turnover cycle). For example, a 20,000-gallon pool needs at least 20,000 / 480 = 41.7 GPM. You would choose a pump rated for at least 42 GPM.
How Long Does It Take to Fill a Pool?
Fill time depends on your water pressure and hose size. A standard garden hose delivers around 500 to 600 gallons per hour, depending on your water pressure.
| Pool Volume | Time at 500 gal/hr | Time at 1,000 gal/hr |
|---|---|---|
| 10,000 gallons | ~20 hours | ~10 hours |
| 15,000 gallons | ~30 hours | ~15 hours |
| 20,000 gallons | ~40 hours | ~20 hours |
| 25,000 gallons | ~50 hours | ~25 hours |
| 30,000 gallons | ~60 hours | ~30 hours |
Using two garden hoses roughly doubles the fill rate. A fire hose hookup from your water supplier (sometimes available for large pools) can fill at 3,000 to 5,000 gallons per hour.
Frequently Asked Questions
How many gallons are in a standard pool?
A standard 16 x 32 ft backyard pool with an average depth of 5 ft holds about 19,200 gallons. Smaller 12 x 24 ft pools hold around 9,700 gallons. Above-ground round pools range from 5,000 to 15,000 gallons depending on size.
How do I calculate how many gallons my pool is?
Use the formula for your pool’s shape. For a rectangle: Length x Width x Average Depth x 7.48 = gallons. For a round pool: 3.14159 x radius squared x depth x 7.48 = gallons. The calculator above handles all shapes automatically.
How many gallons is a 12 x 24 pool?
A 12 x 24 ft rectangular pool with an average depth of 4.5 ft holds about 9,700 gallons. With a 5 ft average depth it holds about 10,800 gallons.
How many gallons is a 15 ft round pool?
A 15 ft diameter round pool that is 4 ft deep holds approximately 5,300 gallons. At 3.5 ft deep it holds about 4,600 gallons.
How many gallons is a 24 ft round pool?
A 24 ft diameter round above-ground pool at 4 ft depth holds approximately 13,500 gallons. At 4.5 ft deep it holds about 15,200 gallons.
How many gallons is a 18 x 36 pool?
An 18 x 36 ft rectangular pool with a 5.5 ft average depth holds approximately 26,600 gallons. With a 5 ft average depth it holds about 24,200 gallons.
Does pool volume include the water in the pipes and filter?
The volume calculated here is for the pool basin only. The water in pipes, the filter tank, and the heater adds roughly 50 to 150 gallons depending on your equipment. For chemical dosing purposes this small addition is generally ignored, but for precise salt or chemical calculations you can add 100 gallons as a rough allowance.
Why do some formulas use 7.5 and others use 7.48?
One cubic foot of water contains exactly 7.48052 US gallons. Many pool guides round this to 7.5 for easier mental math. Our calculator uses the precise value of 7.48 for accuracy. The difference is less than 0.3% and has no practical impact on chemical dosing.
How accurate is a pool volume calculator?
A pool volume calculator is as accurate as the measurements you put in. If you measure your pool carefully, the result will be within 1 to 3% of the actual volume. Irregular shapes like freeform pools have higher uncertainty (5 to 10%) because the formula uses an approximation.
How do I find my pool volume without measuring?
Check your pool construction documents or original installer paperwork. The volume is often listed there. You can also contact your pool builder or the manufacturer of your above-ground pool — they will have the specification on file. If you know the pool’s size but not the depth, a standard depth for residential pools is 4 to 5 ft average.
Quick Tips for Accurate Measurements
- Measure the water surface, not the pool shell. The shell is always slightly larger than the water area, especially on fiberglass pools with integrated coping.
- For above-ground round pools, measure the inside diameter, not the outside. The wall takes up 2 to 4 inches on each side.
- For an irregular shape, take multiple width measurements at different points along the length and average them for a more accurate result.
- Measure depth when the pool is full to its normal operating level (middle of the skimmer). Measuring an empty pool can give incorrect depth if the bottom is uneven.
- Double-check your measurements by measuring twice in different directions. A small error in one dimension compounds into a larger error in the final volume.