Pool Volume Calculator
How many gallons your pool holds, the number every chemical dose starts from, so it's worth getting right.
Why our numbers are more realistic
Pool volume math is simple, but two common shortcuts put many calculators off by 10–15%, and every chemical dose inherits that error.
| Typical calculator | This calculator | Why it matters |
|---|---|---|
| Treats every oval as an ellipse (length × width × depth × 5.9) | Asks whether the oval has straight sides, and if so uses the rounded-ends shape | A 15 × 30 ft straight-sided oval holds about 13–14% more than the ellipse formula says. Intex's published capacity for its 20 × 10 ft oval matches the rounded-ends shape almost exactly; the ellipse formula doesn't fit. |
| Asks for "depth" and gets the wall height | Asks for water depth and warns when you enter a standard wall height | A 48 in wall holds about 42 in of water, so entering 48 in overstates the volume by about 14%. |
How this works
Gallons = surface area × average water depth × 7.48 (gallons per cubic foot).
- Round: 3.14 × diameter² ÷ 4.
- Rectangle: length × width.
- Oval, rounded ends (straight sides): a rectangle plus two half-circles, (length − width) × width + 3.14 × width² ÷ 4.
- Egg-shaped oval: 3.14 × length × width ÷ 4.
- Kidney or freeform: 0.45 × (widest + narrowest width) × length. This is an estimate.
- Water depth: from the floor to the water surface, not to the top of the wall. Pool makers' capacity charts put above-ground water about 6 in below the top, so a 48 in wall holds about 42 in.
- Average depth: (shallow + deep) ÷ 2, which assumes the bottom slopes evenly. Depths in inches are divided by 12 (42 in = 3.5 ft).
Results over 5,000 gallons round to the nearest 100, since pool measurements aren't more precise than that.
Common questions
Is my oval the rounded-ends kind or egg-shaped?
Look at the long sides. If they run straight and the ends are half-circles, pick "Oval, rounded ends". Most above-ground ovals are built that way. If the outline curves all the way around, like an egg, pick "Egg-shaped".
My deep end is short and steep. What do I enter?
Your own average depth, as the water depth, with the deep-end box left blank. Averaging the two ends would read high. For example, if about two-thirds of the pool is 3 ft deep and one-third is 8 ft, the average is about 4.7 ft, not 5.5.
What's the most accurate way to find my pool's volume?
Your pool's manual or the builder's spec sheet, if it lists a capacity. Otherwise, read your water meter before and after a full fill. If the meter reads in cubic feet, multiply by 7.48 for gallons.
Next: adding chemicals (order, waits, test limits)
Order. Adjusting more than one thing? Do alkalinity first, then pH, then chlorine, with the pump running and at least 20 minutes between, retesting as you go. Keep calcium several hours apart from baking soda or soda ash, since together they can cloud the water. Never pour acid and chlorine in together.
| What you added | Retest after | Good to know |
|---|---|---|
| Liquid chlorine or bleach | About 30 minutes, pump on | Swim once a retest reads 4 ppm or below. |
| Cal-hypo shock | About 30 minutes for chlorine | Wait 24 hours before adjusting pH or alkalinity. Swim once a retest reads 4 ppm or below. |
| Acid (muriatic or dry) | 30 minutes to 2 hours, then the next day | pH creeps back up for a day as the water gives off carbon dioxide. Swim once a retest reads between 7.2 and 7.8. |
| Soda ash (pH up) | About 2 hours | Raises alkalinity too. |
| Baking soda | 6 to 24 hours | Run the pump at least 6 hours first. |
| Calcium chloride | 4 to 8 hours of pump time | Recheck chlorine too. |
| Salt | 24 hours, pump on | Brush the bottom so it dissolves. |
| Stabilizer (CYA) | 3 to 5 days | Don’t backwash for 48 to 72 hours. |
The short waits need the pump running; retesting the next day catches slow drift.
What your test can’t tell you.
- Most pH tests read only 6.8 to 8.2, so a reading at either end may be further out.
- Chlorine above about 10 ppm throws off the pH test and can bleach a chlorine drop test to a false low. Color-match DPD chlorine tests read only to about 5 ppm; an FAS-DPD drop test reads higher.
- Many kits can’t read stabilizer below about 20 ppm.
- Salt generator displays can be off by about 500 ppm; check with a salt test.
- Test strips read calcium only roughly; use a drop kit.
After heavy rain or an overflow, test free chlorine, pH, alkalinity and stabilizer before adding anything. Rain dilutes the water and can move pH either way, so test rather than guess. Strong sun and heat burn chlorine off faster, so in a hot, sunny climate test chlorine daily.
Filling from a well? Test the fill water at the spigot for metals first. Above about 0.2 ppm copper or 0.3 ppm iron, chlorine can turn the metals into stains. Add a metal sequestrant before you chlorinate, wait 3 to 4 days before shocking, and avoid copper-based algaecides.
From: Swim University on chemical order, Trouble Free Pool on adding chemicals, Trouble Free Pool on pH, Taylor Technologies FAQ, Swim University on metals and Trouble Free Pool on metals, plus the product labels and manuals in Sources.
What this doesn't cover
- L-shaped pools: split the L at the inside corner into two rectangles that don't overlap, work out each one as a rectangle, and add the gallons.
- Steps, benches, and sun shelves, which displace a little water.
- Spas and hot tubs, which are best taken from the manufacturer's spec.
Sources
- Intex 20 ft × 10 ft × 48 in Prism Frame oval pool: 20 × 10 × 48 in oval listed at 4,809 gal at 90% fill, matching the rounded-ends formula.
- City of Akron pool fill chart: oval capacities using length × width × depth × 5.9, the ellipse formula many calculators use.
- 1 cubic foot = 1,728 cubic inches, and a US gallon is 231 cubic inches, so 1 cu ft ≈ 7.48 gal.
Numbers last reviewed: October 9, 2026.