Enter your pool's shape and depth and get the water volume in gallons. It handles
rectangular, round, and oval pools, and a floor that's either a constant depth or
sloped from a shallow end to a deep end. The math is plain geometry times
7.48052 — the number of US gallons in a cubic foot.
Volume in gallons·Rectangular, round & oval·Constant or sloped depth
Read this first
This is a geometric estimate, not an exact measurement. Real pools have steps, benches,
swim-outs, rounded corners, and hoppers that change the true volume, so treat the number
as a close approximation. It's plenty accurate for picturing your pool's size or sizing
equipment, but for anything that has to be exact, confirm against your builder's
specifications. The chemical figures further down are rough starting estimates only
— always follow the dosing instructions on the product label.
Pick a shape and a depth mode, enter your measurements in feet, and you'll get the water volume in gallons (plus the volume in cubic feet and the average depth used).
Shape
The distance straight across the pool at its widest.
Across the longest axis.
Across the shortest axis.
Depth
The water depth, the same everywhere.
We average the two for a steady-grade floor.
Water volume (gallons)
Volume (cubic feet)
Average depth used
Approx. shock estimate
The math, honestly
How the gallons are figured
It's surface area times depth times a unit conversion. First find the
surface area of the water: for a rectangle it's
length × width; for a round pool it's
π × (diameter/2)²; for an oval it's
π × (length/2) × (width/2). Everything is measured in feet.
Next, multiply by the average depth to get the volume in cubic feet.
If the floor is flat, the average depth is just the depth. If it slopes from a shallow
end to a deep end, average them: (shallow + deep) / 2. A pool 3 ft at the
shallow end and 8 ft at the deep end has an average depth of 5.5 ft.
Finally, convert cubic feet to gallons by multiplying by 7.48052, the
number of US gallons in a cubic foot. So a 32 ft × 16 ft rectangular pool with a
5 ft average depth holds 32 × 16 × 5 × 7.48052 ≈ 19,150
gallons, and a 24 ft round pool 4 ft deep holds
π × 12² × 4 × 7.48052 ≈ 13,536 gallons.
Common pool sizes
Approximate water volumes for some common pool sizes, computed with the same formula the
calculator uses (surface area × average depth × 7.48052) and rounded to the
nearest 10 gallons. Your own pool may differ with steps, benches, and a hopper.
Pool
Shape
Avg depthfeet
Approx. gallonsUS gallons
24 × 12 ft
Rectangular
4
8,620
32 × 16 ft
Rectangular
5
19,150
40 × 20 ft
Rectangular
5.5
32,910
15 ft diameter
Round
4
5,290
18 ft diameter
Round
4
7,610
24 ft diameter
Round
4
13,540
15 × 30 ft
Oval
5
13,220
16 × 32 ft
Oval
5
15,040
Gallons are rounded to the nearest 10. Round and oval figures treat the pool as a perfect
circle or ellipse at the water surface; real liners and walls vary slightly. Use the
calculator for your exact dimensions.
A rough sense of chemicals
Once you know the gallons, you can picture roughly how much product a job takes. The
figure below is an order-of-magnitude estimate only, included so the
volume number feels concrete — it is not dosing advice.
Estimate only — not dosing advice
How much shock, roughly?
A common rule of thumb for routine shocking with cal-hypo (calcium hypochlorite)
shock is about 1 pound per 10,000 gallons. So a 20,000-gallon pool
would be in the neighborhood of 2 pounds, and a 13,500-gallon pool
around 1.4 pounds. The calculator shows this same rough figure for
your pool's volume.
This is only a starting point to picture scale. The real amount depends on the specific
product and its strength, the current chlorine and stabilizer levels, the water
temperature, and why you're shocking (routine maintenance versus clearing algae). Some
products use very different doses, and over-shocking can damage liners and equipment.
Always follow the dosing instructions printed on the product label.
This is a rough starting estimate to picture scale, not dosing advice. When in doubt,
test your water and ask a pool professional.
Reading the result well
A gallon figure is only useful if you know what it does and doesn't tell you. Four things
worth keeping in mind.
It's an estimate, not a survey
The math treats your pool as a clean geometric shape with a steady-grade floor. Steps, tanning ledges, benches, swim-outs, rounded corners, and a deep-end hopper all change the true volume — usually making it a little less than the raw calculation. For sizing a heater, a cover, or chemicals, the estimate is fine. For anything that must be exact, use your builder's specs.
Average depth is the trick for sloped floors
A pool that slopes from shallow to deep holds the same water as a flat pool at the average of those two depths — as long as the slope is steady. If your pool has a flat shallow section followed by a sudden drop into a deep hopper, the simple average overstates the volume a bit. Measuring at a few points and averaging gets you closer.
Round and oval are just circles
A round pool's surface is a circle, so area is π times the radius squared. An oval is a stretched circle, so area is π times half the length times half the width. Both then multiply by average depth and by 7.48052. If your pool is a kidney or freeform shape, approximate it by breaking it into a rectangle plus a half-circle, or treat it as the nearest oval.
Why the gallon number matters
Almost every pool decision scales with volume: chemical doses, heater and pump sizing, how long it takes to fill, and how much a leak is costing you. Knowing the gallons turns a vague "it's a big pool" into a number you can plan around. Keep it written down somewhere — you'll reach for it more than you'd expect.
Where to buy
Got your numbers? Here's where to pick up what you need:
The terms behind the calculator, in plain English. These are background definitions for a
volume estimate — not water-chemistry or equipment-sizing advice.
US gallon
The volume unit pools are usually measured in for chemicals and equipment. One cubic foot of water is 7.48052 US gallons, so multiplying a pool's volume in cubic feet by 7.48052 converts it to gallons.
Cubic foot
A cube one foot on each side. It's the working unit for pool volume: surface area in square feet times average depth in feet gives cubic feet, which you then convert to gallons.
Average depth
The single depth that, applied to the whole pool, gives the same volume as the real sloped floor. For a steady slope it's the shallow depth plus the deep depth, divided by two. For a flat floor it's just the depth.
Surface area
The area of the water's surface, in square feet. For a rectangle it's length × width; for a round pool it's π times the radius squared; for an oval it's π times half the length times half the width. Multiply it by average depth to get volume.
Hopper
The bowl-shaped deep section of a pool where the floor drops below the steady slope. A hopper makes the simple shallow-plus-deep average slightly overstate the volume, because the deep end isn't a full rectangle — it's a tapered bowl.
Cal-hypo shock
Calcium hypochlorite, a common granular pool shock. A frequently cited rule of thumb is about 1 lb per 10,000 gallons for routine shocking — but this is a rough starting estimate only. Actual dosing depends on the product and water conditions, so always follow the product label.
Freeform pool
A pool with an irregular, curving shape — kidney, lagoon, or custom. It has no single clean formula, so volume is estimated by breaking it into simpler shapes (a rectangle plus a half-circle, say) or approximating it as the nearest rectangle or oval.
Frequently asked
It depends on the surface area and the average depth. Find the volume in cubic feet first — length × width × average depth for a rectangle, or π × radius² × average depth for a round pool — then multiply by 7.48052, the gallons in a cubic foot. For example, a 32 ft × 16 ft pool with a 5 ft average depth holds 32 × 16 × 5 × 7.48052 ≈ 19,150 gallons. The calculator does this for your own shape and depth.
Work out the volume in cubic feet, then multiply by 7.48052 gallons per cubic foot. The volume in cubic feet is the surface area times the average depth. Surface area is length × width for a rectangle, π × radius² for a round pool, or π × (length/2) × (width/2) for an oval. If the floor slopes, use the average of the shallow-end and deep-end depths. Measure everything in feet first.
For a pool that slopes evenly from a shallow end to a deep end, the average depth is the shallow depth plus the deep depth, divided by two. A pool that's 3 ft shallow and 8 ft deep has an average depth of (3 + 8) / 2 = 5.5 ft. Averaging treats the sloped floor as if it were flat at that depth, which is accurate for a steady grade. Pools with a flat shallow section, a sudden drop, or a deep hopper are only approximated this way.
As a rough starting estimate, many cal-hypo shock products suggest about 1 lb per 10,000 gallons for routine shocking, so a 20,000-gallon pool would need roughly 2 lb. That's only an order-of-magnitude figure. The right dose depends on the specific product and its strength, the current chlorine level, the water temperature, and why you're shocking. Always follow the dosing instructions printed on the product label — this page is not dosing advice.
A round pool has a single diameter, so its surface area is π × radius², where the radius is half the diameter. An oval pool has a longer length and a shorter width, so its area is π × (length/2) × (width/2). In both cases you then multiply by the average depth and by 7.48052 to get gallons. The only difference is the surface shape: one circle versus a stretched circle. The calculator has a mode for each.
There are exactly 7.48052 US gallons in one cubic foot, so multiplying a volume in cubic feet by 7.48052 converts it to gallons. Many calculators round this to 7.48, which is close enough for most uses; this tool keeps the fuller figure so large pools stay accurate. The constant is a fixed unit conversion — it doesn't change with water temperature or pool type.
It's a close estimate, not an exact measurement. The math treats the pool as a clean geometric shape with a steady-grade floor, but real pools have rounded corners, steps, benches, swim-outs, and hoppers that change the true volume. For most uses — sizing a heater or picturing chemical doses — the estimate is good enough. When a precise figure matters, confirm it against your pool builder's specifications.
Common mistakes
Pool volume estimates are only as good as the measurements that go in. These four errors
are the most common reasons the calculated gallons don't match reality.
Using the deep-end depth instead of the average depth
A pool with a 3 ft shallow end and an 8 ft deep end holds water equal to a flat-bottomed pool at the average — 5.5 ft — not at 8 ft. Using the deep-end depth overstates the volume significantly. The sloped-floor mode in the calculator averages the two depths automatically; if you enter a single depth, make sure it is the average of shallow and deep, not the maximum.
Entering the radius instead of the diameter for a round pool
Round-pool volume uses π × radius², where the radius is half the diameter. If you measure "24 feet across" and enter 24 as the radius rather than the diameter, the calculated volume is four times too large. Measure straight across the widest point of the pool — that is the diameter. The calculator handles the radius internally when you enter the diameter.
Expecting the geometric estimate to match the actual fill volume exactly
Steps, tanning ledges, benches, swim-outs, rounded corners, and a deep-end hopper all reduce the real water volume below the clean-geometry formula's result. For most uses — sizing a heater or estimating chemical doses — the geometric estimate is accurate enough. When a precise figure matters, use the volume from the pool builder's specification sheet.
Using the shock estimate as a dosing instruction
The "1 lb of cal-hypo per 10,000 gallons" figure is an order-of-magnitude illustration to make the volume feel concrete. It is not a dosing instruction. The correct amount depends on the product's specific chlorine concentration, the current free chlorine level in the water, cyanuric acid (stabilizer) level, water temperature, and the reason for shocking. Always follow the dosing instructions printed on the product label.