Pool Volume Calculator: How Many Gallons is My Pool?
Calculate how many gallons your pool holds with our free Pool Volume Calculator. Simply choose your pool shape and enter the dimensions for instant, accurate water volume results. Let’s start!
Table of Contents
How Many Gallons Is Your Pool?
Multiply length × width × average depth (all in feet) to get cubic feet, then multiply by 7.48 to convert to gallons. A standard 32×16 ft rectangular pool at a 5.5 ft average depth holds about 21,113 gallons. For a round pool, use π × radius² instead of length × width. Always measure the actual water depth, not the wall height — most pools aren’t filled to the brim. Use the calculator below for your exact shape and dimensions.
Pool Volume Calculator
Finds your pool’s volume in gallons for rectangular, round, oval, or kidney shapes, plus liters, UK gallons, and a pump turnover tip.
Every pool chemical decision starts with one number: gallons. Get it wrong and you’ll either under-dose chlorine and watch algae move in, or over-dose and waste money on chemicals you didn’t need. The formula itself isn’t hard. It’s the details — average depth, pool shape, the right conversion factor — where most people trip up.
Why Pool Volume Matters More Than You’d Think
It’s tempting to just eyeball a dose or follow the label’s “average pool” instructions. But every dosage — chlorine, acid, shock, salt — gets calculated against your actual gallon count. Pump sizing, filter sizing, and heater selection all depend on this same number too. So get the volume wrong once, and it throws off pretty much every maintenance decision you make after that.
The Basic Formula, Step by Step
Here’s the math for a standard rectangular pool.
Example: say you have a rectangular pool, 32 ft long, 16 ft wide, with a 3.5 ft shallow end and a 7.5 ft deep end.
1. Find your average depth: (3.5 + 7.5) ÷ 2 = 5.5 ft.
2. Find your surface area: 32 ft × 16 ft = 512 sq ft.
3. Find your volume in cubic feet: 512 sq ft × 5.5 ft = 2,816 cubic feet.
4. Convert to gallons: 2,816 × 7.48 = 21,064 gallons.
So: that’s a pretty typical in-ground pool size, and this gallon figure is exactly what you’d plug into any chlorine, shock, or salt dosing chart.
Formulas by Pool Shape
The core idea stays the same no matter what shape you have — surface area × average depth × 7.48. What changes is how you find the surface area.
| Shape | Area Formula | Full Volume Formula |
|---|---|---|
| Rectangular | Length × Width | L × W × Avg Depth × 7.48 |
| Round | π × Radius² | π × r² × Avg Depth × 7.48 |
| Oval | π × (L÷2) × (W÷2) | π × (L÷2) × (W÷2) × Avg Depth × 7.48 |
| Kidney | L × Widest W × 0.585 | L × W × 0.585 × Avg Depth × 7.48 |
Volume Reference by Common Pool Size
Here’s a quick reference table assuming typical average depths. Use the calculator above if you want your exact numbers.
| Pool Size | Shape | Avg Depth | Approx. Volume |
|---|---|---|---|
| 18 ft diameter | Round | 4 ft | ~7,621 gal |
| 24 ft diameter | Round | 4.5 ft | ~15,290 gal |
| 24 × 12 ft | Rectangular | 5 ft | ~10,771 gal |
| 32 × 16 ft | Rectangular | 5.5 ft | ~21,113 gal |
| 32 × 16 ft | Kidney | 5 ft | ~11,218 gal |
Finding Average Depth on a Sloped Pool
Most in-ground pools aren’t one flat depth — they slope from a shallow end down to a deeper end. So just add the shallow end depth to the deep end depth and divide by two. That gives you a usable average, as long as the slope between them is fairly gradual and even.
Above-ground pools and some smaller in-ground designs have one flat depth throughout. No averaging needed — just use that single number.
Use the shallow-plus-deep-divided-by-two average. If you’ve got a steep or hopper-bottom profile, splitting the pool into sections gets you a more accurate result.
What Your Volume Number Actually Controls
Once you’ve got an accurate gallon count, it feeds directly into a bunch of other decisions:
- Chemical dosing — chlorine, shock, acid, and salt are all measured against your total gallons.
- Pump sizing — your pump should turn over the entire pool volume at least once every 8 hours.
- Filter sizing — an undersized filter just can’t keep up with the flow rate your volume needs.
- Heater sizing — BTU requirements for a pool heater scale directly with how much water you’re warming.
Handling Irregular or Freeform Shapes
Got a pool that doesn’t fit a standard shape — L-shaped, T-shaped, stepped, or freeform? Break it into simpler sections. Calculate each rectangle, circle, or triangle separately using the formulas above, then add all the section volumes together for your total. This same divide-and-conquer trick works for almost any unusual layout.
Common Pool Volume Mistakes
Measuring wall height instead of water depth. Most pools aren’t filled to the brim, so using wall height overestimates your volume and leads to over-dosing chemicals.
Rounding your measurements too early. Rounding area and then volume separately stacks small errors into a final number that’s noticeably off.
Using one single depth on a sloped pool. Skip the shallow-plus-deep average and you’ll meaningfully over- or underestimate your true volume.
Treating a kidney or freeform pool like a rectangle. These shapes need their own formula or a section-by-section breakdown. A straight L×W calculation overstates the real volume.
Not re-measuring after adding features. Steps, benches, and tanning ledges all reduce your actual water volume compared to the pool’s outer dimensions.
Not sure of your exact gallons? Use the Pool Volume Calculator above for rectangular, round, oval, or kidney shapes, plus a quick pump turnover recommendation based on your total.
Why trust this guide: these formulas and conversion factors reflect standard calculations used across pool industry and maintenance references. If your pool has an unusual shape, or you’re relying on this number for something big like a large chemical order, it’s worth having a pool pro verify the measurement.
So that’s really all there is to it. I hope this saves you the pencil-and-paper math next time you’re dosing chemicals or sizing equipment. If your pool has an unusual shape that doesn’t fit neatly into these categories, drop a comment below and I’ll help you work through it.
Frequently Asked Questions
At a 5.5 ft average depth, a 32×16 ft rectangular pool holds approximately 21,113 gallons. The exact number shifts depending on your actual shallow and deep end measurements.
Volume is the foundation for almost every pool maintenance decision — chemical dosing (chlorine, acid, shock, salt), pump sizing, filter sizing, and heater selection all depend directly on knowing how many gallons you’re working with.
Always use the actual water depth, not the wall height. Most pools aren’t filled all the way to the top, so using wall height will noticeably overestimate your volume and lead to over-dosing chemicals.
Add the shallow end depth to the deep end depth, then divide by 2. For example, a 3.5 ft shallow end and a 7.5 ft deep end average out to 5.5 ft, assuming a fairly even, gradual slope between them.
A common approach multiplies length by the widest width, then by a 0.585 shape factor to account for the curved, non-rectangular footprint, before multiplying by average depth and the gallon conversion factor.
Break the pool down into simpler geometric sections — rectangles, circles, or triangles — calculate each section’s volume separately, then add them together for your total. This works for L-shaped, T-shaped, and stepped pools too.
This is a standard volume conversion — one cubic foot of water contains 7.48 US gallons. Some sources round this to 7.5 for simplicity, which introduces only a tiny rounding difference on most residential pool sizes.
A common rule of thumb is that your pump should be able to turn over the entire pool volume at least once every 8 hours. Dividing your total gallons by 480 minutes gives you the minimum flow rate (GPM) your pump needs to handle.
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