How to calculate pool volume
Every pool chemical dose, heater size and pump turnover starts with one number: how many gallons the pool holds. You find it the same way for any shape: the surface area times the average depth gives cubic feet, and each cubic foot holds 7.48 gallons. Here it is with the values the calculator opens with: a 16 x 32 ft rectangle, 3.5 ft at the shallow end and 6 ft at the deep end.
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1
Find the average depth
Add the shallow and deep ends and divide by 2. (3.5 + 6) ÷ 2 = 4.75 ft.
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2
Find the surface area
For a rectangle, length times width: 32 × 16 = 512 sq ft.
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3
Multiply for cubic feet
512 sq ft × 4.75 ft = 2,432 cubic feet.
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4
Convert to gallons
2,432 × 7.48 = 18,193 gallons. In metric, 2,432 cubic feet is 68.9 cubic meters, or 68,867 liters.
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5
Price the fill
18,193 gallons at $10.50 per 1,000 gallons is $191. At 10 gallons a minute from a garden hose, that's 1,819 minutes, about 30 hours.
That pool also weighs a lot: water is 8.34 pounds a gallon, so 18,193 gallons is about 76 tons. It's why an above-ground pool needs dead-level, compacted ground and why you should never drain an in-ground pool without asking a pro about groundwater first.
Formulas for each pool shape
Use feet for every measurement and the average depth. Each formula already includes the 7.48 gallons per cubic foot.
| Shape | Gallons = |
|---|---|
| Rectangle or square | length × width × avg depth × 7.48 |
| Round | diameter × diameter × depth × 5.88 |
| Oval | length × width × avg depth × 5.88 |
| Kidney or free-form | (wide end + narrow end) × length × avg depth × 3.37 |
The 5.88 is 7.48 × π ÷ 4, the area of a circle from its diameter. Many pool stores round it to 5.9. The kidney factor (0.45 × 7.48) is an approximation used across the pool trade; free-form pools vary, so treat the result as within about 10%. For an L-shaped pool, split it into two rectangles and add them. If the deep end is a short hopper instead of a long slope, the simple average overstates the volume a little.
Gallons in common pool sizes
In-ground rectangles from 3.5 to 6 ft deep (4.75 ft average). Above-ground pools filled to 4 ft of water, typical for a 52-inch wall. Tap a size to load it.
| Pool | Gallons | Liters |
|---|---|---|
| 12 x 24 in-ground | 10,233 | 38,737 |
| 14 x 28 in-ground | 13,929 | 52,726 |
| 16 x 32 in-ground | 18,193 | 68,867 |
| 18 x 36 in-ground | 23,025 | 87,159 |
| 20 x 40 in-ground | 28,426 | 107,604 |
| 15 ft round | 5,288 | 20,016 |
| 18 ft round | 7,614 | 28,823 |
| 21 ft round | 10,364 | 39,231 |
| 24 ft round | 13,536 | 51,241 |
| 27 ft round | 17,132 | 64,852 |
| 15 x 30 oval | 10,575 | 40,032 |
| 18 x 33 oval | 13,959 | 52,842 |
What it costs to fill, and how long it takes
Water is cheap by the gallon but a pool uses a lot of gallons. U.S. water and sewer bills averaged $86.41 a month for 4,800 gallons and $101.14 for 6,200 gallons in a 2025 national survey of 414 utilities. The difference works out to about $10.50 per extra 1,000 gallons, which is the calculator's default. Rates vary several-fold by city, so check your bill: most list the price per 1,000 gallons or per CCF (748 gallons).
About half of that is usually sewer. Water that goes into a pool never reaches the sewer, and many utilities will waive or credit the sewer charge for a pool fill if you call before you start. Some also install a temporary meter. It's worth a phone call on a pool this size.
A typical 5/8-inch garden hose delivers about 9 to 12 gallons a minute at normal house pressure, less on a long hose or a weak well. To measure yours, time how long it takes to fill a 5-gallon bucket: 30 seconds means 10 gallons a minute. Two hoses on two spigots fill about twice as fast. A bulk water truck is another option, often used where wells can't keep up; it fills a pool in hours but usually costs more per gallon than city water.
Chlorine doses by volume
Dosing is plain math once you know the volume. One part per million (ppm) is one milligram per liter, so raising 10,000 gallons (37,854 liters) by 1 ppm takes about 38 grams of available chlorine. What you pour in depends on the product's strength:
| Per 10,000 gallons | +1 ppm | +10 ppm (shock) |
|---|---|---|
| Liquid chlorine 12.5% | 10.2 fl oz | 0.8 gallon |
| Liquid chlorine 10% | 12.8 fl oz | 1 gallon |
| Cal-hypo shock 65% | 2.05 oz | 1.28 lb |
The CDC recommends keeping free chlorine at least 1 ppm in a home pool, or at least 2 ppm if you use cyanuric acid (stabilizer), with pH between 7.0 and 7.8. Outdoor pools need stabilizer because sunlight burns off unprotected chlorine within hours; 30 ppm is a common starting level, and the calculator adds enough to reach it. A common shock dose on product labels is 1 pound of 65% cal-hypo per 10,000 gallons, which works out to about 7.8 ppm.
- Follow the label. Pool chemicals are EPA-registered pesticides, and the label is the legal dose. These numbers help you check it against your real volume.
- Never mix chemicals. Add each one separately to the pool water, never water to chemical, and never put cal-hypo and trichlor or acid together. The reaction can start a fire or release chlorine gas.
- Test, then dose. A drop-test kit measures free chlorine more accurately than strips. Shock in the evening with the pump running, and wait until free chlorine is back in range before swimming.
- Household bleach works, but it's only about half as strong as pool chlorine and must be unscented and free of additives.
Tips from pool pros
- Measure the water, not the pool. In-ground pools are filled to the middle of the skimmer opening, about 6 inches below the coping. Above-ground pools usually sit 6 inches below the top rail.
- Write the number down. Put the gallons on the pump or in your phone. You'll use it every time you add salt, acid, stabilizer or algaecide.
- Fill with a hose filter if your water is from a well. Metals like iron and copper can stain the plaster or liner as soon as you add chlorine.
- Keep the hose end in the water. Set it so it can't siphon back, and never leave the fill running unattended overnight on a vinyl pool, where an overfill can float the liner.
- Know your turnover. Most pool codes and pump guides aim to move the whole volume through the filter in about 6 to 8 hours. Divide the gallons by the hours to get the flow the pump needs.
Draining and refilling a pool, resurfacing, and any electrical work on pumps, heaters or lights are jobs for a licensed pool contractor or electrician. Pool and spa wiring has its own section of the National Electrical Code for good reason.
Common questions
How do I calculate how many gallons are in my pool?
Find the volume in cubic feet and multiply by 7.48, the number of gallons in a cubic foot. For a rectangle, multiply length by width by average depth. For a round pool, multiply the radius squared by 3.14 and by the depth. The average depth is the shallow end plus the deep end, divided by 2.
How many gallons is a 16x32 pool?
A 16 by 32 foot pool that goes from 3.5 feet to 6 feet deep has an average depth of 4.75 feet. That is 2,432 cubic feet, or about 18,200 gallons (68,900 liters). A pool with an 8-foot deep end holds about 22,000 gallons.
How many gallons is a 24-foot round pool?
A 24-foot round above-ground pool filled to 4 feet of water, typical for a 52-inch wall, holds about 13,500 gallons (51,200 liters). Each extra 6 inches of water adds about 1,700 gallons.
How much does it cost to fill a pool?
At about $10.50 per 1,000 gallons, a rough U.S. average for water plus sewer at the margin, an 18,000-gallon pool costs about $190 to fill. Many utilities waive sewer charges for pool filling if you ask first, which can cut the cost roughly in half.
How long does it take to fill a pool with a garden hose?
A typical 5/8-inch garden hose delivers about 9 to 12 gallons a minute. At 10 gallons a minute, an 18,000-gallon pool takes about 30 hours. Time how long your hose takes to fill a 5-gallon bucket to find your real flow.
How much chlorine do I need for my pool?
Raising free chlorine by 1 ppm in 10,000 gallons takes about 38 grams of chlorine: roughly 10 fluid ounces of 12.5% liquid chlorine or 2 ounces of 65% calcium hypochlorite. The CDC recommends at least 1 ppm in pools, or at least 2 ppm if you use stabilizer. Always follow the product label.
How much shock do I need per gallon?
A common label dose for 65% calcium hypochlorite shock is 1 pound per 10,000 gallons, which raises free chlorine by about 7.8 ppm. With 12.5% liquid chlorine, about 0.8 gallons per 10,000 gallons raises it by 10 ppm. Follow the label of the product you buy.
Sources and assumptions
- Volume formulas: geometry with 7.48052 gallons per cubic foot and 28.317 liters per cubic foot. The kidney factor of 0.45 follows Leslie's guide to calculating pool volume, which uses 7.5 gallons per cubic foot.
- Water price: $10.50 per 1,000 gallons is the marginal water and sewer price implied by the national averages ($86.41 at 4,800 gallons, $101.14 at 6,200 gallons a month: $14.73 for 1,400 more gallons, or $10.52 per 1,000) in the 2025 wave of Manny Teodoro's biennial water and sewer affordability survey of 414 U.S. utilities (published August 2026). Your local rate may be far higher or lower.
- Hose flow: 10 gallons a minute is an estimate for a 5/8-inch hose at 40 to 60 psi; published figures range from about 9 to 17 gpm. Measure yours with a bucket.
- Chlorine levels: CDC, Home Pool and Hot Tub Water Treatment and Testing (at least 1 ppm free chlorine, 2 ppm with cyanuric acid, pH 7.0 to 7.8).
- Doses: 1 ppm = 1 mg per liter of available chlorine. Liquid strengths are taken as grams per 100 mL (trade percent); cal-hypo as 65% available chlorine by weight. The 1 lb per 10,000 gallon shock rate is printed on EPA-registered cal-hypo labels; search them in the EPA Pesticide Product Label System. Stabilizer is counted as 100% cyanuric acid.
- Chemical prices (October 2026 estimates, all editable except stabilizer): liquid chlorine about $8 per gallon for 12.5% and $6 for 10% (store prices range from about $5 to $15), cal-hypo about $6 per pound in multi-packs, stabilizer $5 per pound. The opening list rounds liquids up to whole gallons and solids to whole pounds.