Pool Volume Calculator — Gallons
Find your pool's volume in US gallons using exact shape formulas, a size reference table, and step-by-step conversion examples.
How to Calculate Pool Volume in Gallons
Multiply the pool's cubic-foot volume by 7.48052 to convert to US gallons. The multiplier 7.48052 represents the exact number of US gallons in one cubic foot of water. Every pool shape uses the same conversion factor in the final step — only the area formula changes.
| Pool Shape | Formula (US Gallons) |
|---|---|
| Rectangular | L × W × Avg Depth × 7.48052 |
| Round | D² × 0.7854 × Depth × 7.48052 |
| Oval | L × W × 0.7854 × Depth × 7.48052 |
Three pool shapes account for 95% of residential swimming pools in the US and Canada. Rectangular pools use a straight length × width × average depth calculation. Round pools replace length and width with the diameter squared times 0.7854 (the value of π ÷ 4). Oval pools apply the same 0.7854 constant to the longest and widest inside measurements.
Average depth matters more than wall height. A pool with a 3 ft shallow end and an 8 ft deep end has an average depth of 5.5 ft — not the 8 ft a homeowner might assume from the diving area. Using 8 ft instead of 5.5 ft overestimates volume by 45%, which throws off every chemical dose for the season.
Pool chemical labels assume the pool is filled to the marked waterline — not to the top of the wall. Always calculate from actual water depth.
Measure water depth with a weighted string dropped from the pool edge to the bottom at 3 points: the shallow end, the centre, and the deep end. Add the 3 readings and divide by 3 to get the average. This method corrects for sloped floors, hopper bottoms, and irregular transitions between shallow and deep zones.
For above-ground pools and any pool with a flat bottom, a single depth measurement is enough. Enter that number directly without averaging.
What Makes US Gallons the Standard
The US gallon (3.785 litres) is the standard unit for pool volume in the United States and for most pool equipment manufactured in North America. Chemical labels, pump flow rates, and filter sizing all reference US gallons. Choosing the wrong gallon type skews every measurement downstream.
| From | To | Multiply By |
|---|---|---|
| 1 cubic foot | US gallons | 7.48 |
| 1 cubic foot | Imperial gallons | 6.23 |
| 1 US gallon | Litres | 3.785 |
| 1 US gallon | Imperial gallons | 0.833 |
| 1 cubic metre | US gallons | 264.17 |
The US gallon (3.785 L) and the imperial gallon (4.546 L) differ by 20%. A pool owner in Canada using an imperial-gallon chemical label on a pool measured in US gallons will overdose by that same 20%. That overshoot pushes chlorine from a target of 3 ppm to 3.6 ppm — above the recommended 1–3 ppm range for residential pools.
The discrepancy traces back to different historical definitions. The US gallon equals 231 cubic inches; the imperial gallon equals 277.42 cubic inches (defined as the volume of 10 pounds of water at 62 °F). Pool equipment sold in the US, Canada, and Mexico standardises on the US gallon.
To convert between units: multiply US gallons by 0.8327 to get imperial gallons, or multiply imperial gallons by 1.20095 to get US gallons. When in doubt, check whether the label prints "US gal" or "Imp gal" — most North American pool chemical brands print "US gal" or simply "gal," which defaults to US.
Pool Volume in Gallons — Common Sizes Reference
The table below lists 8 common residential pool sizes with pre-calculated volumes in US gallons and litres. All figures use the geometric formula for each shape multiplied by 7.48052.
| Pool Size | Shape | Avg Depth | US Gallons | Litres |
|---|---|---|---|---|
| 10 × 20 ft | Rectangular | 4.5 ft | 6,732 | 25,488 |
| 12 × 24 ft | Rectangular | 4.5 ft | 9,699 | 36,722 |
| 16 × 32 ft | Rectangular | 5.5 ft | 21,059 | 79,708 |
| 16 × 32 ft | Rectangular | 6.0 ft | 22,974 | 86,955 |
| 20 × 40 ft | Rectangular | 5.5 ft | 32,934 | 124,654 |
| 18 ft dia | Round | 4.5 ft | 8,565 | 32,418 |
| 24 ft dia | Round | 5.0 ft | 16,965 | 64,211 |
| 28 ft dia | Round | 5.5 ft | 25,365 | 96,007 |
Calculated using shape formula × 7.48052. Litres = US gallons × 3.78541.
For custom pool sizes not listed here, use the pool volume by size lookup or enter your dimensions into the homepage calculator.
How to Calculate by Shape in Gallons
Walk through a complete calculation for a 16 × 32 ft rectangular pool with a 5.5 ft average depth.
Step 1 — Calculate Surface Area
16 × 32 = 512 sq ft
Step 2 — Calculate Volume in Cubic Feet
512 × 5.5 = 2,816 cu ft
Step 3 — Convert to US Gallons
2,816 × 7.48052 = 21,059 gallons
Step 4 — Convert to Litres
21,059 × 3.78541 = 79,708 litres
Result: 21,059 gallons (79,708 litres).
Round pools follow the same 4-step process but replace Step 1 with D² × 0.7854. An 18 ft round pool: 18² × 0.7854 = 254.47 sq ft, then 254.47 × 4.5 = 1,145.1 cu ft, then 1,145.1 × 7.48052 = 8,565 gallons (32,418 litres). Use the round pool volume calculator to run this instantly.
Oval pools use the major axis as length and the minor axis as width, then apply the 0.7854 constant before following Steps 2–4. Rectangular pool calculations skip the 0.7854 step entirely since there is no curve to account for.
For detailed breakdowns of every shape formula, see pool volume formulas for all shapes. To calculate chemical doses based on your result, use the pool chemical dosing calculator.
Frequently Asked Questions
How do I calculate pool volume in US gallons?
Measure the pool's length, width, and average water depth in feet, then multiply by the shape constant and 7.48052. For a rectangular pool the formula is L × W × Avg Depth × 7.48052. A 16 × 32 ft pool at 5.5 ft average depth equals 2,816 cubic feet, which converts to 21,059 gallons (79,708 litres). Round and oval pools replace length × width with the 0.7854 circle constant applied to the diameter.
What is the difference between US gallons and imperial gallons?
A US gallon holds 3.785 litres while an imperial gallon holds 4.546 litres — a 20% difference. Canada and the UK historically used imperial gallons, so chemical labels from those markets assume a larger gallon. Dosing chlorine based on imperial gallons into a pool measured in US gallons adds 20% more chemical than intended. Confirm which gallon the product label references before mixing.
How many gallons does a standard pool hold?
Between 6,700 and 33,000 gallons (25,400–124,900 litres) depending on shape and depth. A 10 × 20 ft rectangular pool at 4.5 ft average depth holds 6,732 gallons (25,488 litres). A 20 × 40 ft pool at 5.5 ft depth holds 32,934 gallons (124,654 litres). Round pools range from 8,565 gallons for an 18 ft diameter to 25,365 gallons for a 28 ft diameter.
Why does pool volume in gallons matter for chemical dosing?
Chlorine, pH adjuster, and algaecide doses are all calculated per 10,000 gallons of water. Overestimating volume by 2,000 gallons adds 20% too much chlorine — enough to bleach vinyl liners and irritate skin. Underestimating by the same margin leaves water under-sanitized, allowing algae to bloom within 48 hours in summer heat. Measure actual water depth — not wall height — because most pools fill 2–4 inches below the top rail.
How do I convert pool volume from cubic feet to gallons?
Multiply the volume in cubic feet by 7.48052 to get US gallons. One cubic foot of water equals exactly 7.48052 US gallons. A pool measuring 2,816 cubic feet holds 2,816 × 7.48052 = 21,059 gallons (79,708 litres). To convert to litres directly, multiply cubic feet by 28.3168. The 7.48052 factor comes from the US gallon definition of 231 cubic inches per gallon.
Should I use 7.48 or 7.5 gallons per cubic foot?
Use 7.48052 for the most accurate result. The rounded 7.5 value overstates volume by 0.27%, adding 57 extra gallons to a 21,000-gallon pool. For chemical dosing, 57 gallons shifts chlorine concentration by less than 0.01 ppm — negligible in practice. For ordering a fill-water delivery, use 7.48 to avoid overpaying. The two-decimal 7.48 understates volume by only 0.007%, making it the best shorthand for most calculations.