Pool Volume Calculator: Gallons, Fill Time, Pump and Chemicals
Shape, size and the shallow and deep end, and it returns gallons plus everything that hangs off gallons. Round and oval pools are figured as round and oval, not as a rectangle, which is where most pool numbers go wrong by about a quarter.
When the figures look right, the pool water and chemical list downloads as a real PDF with your business details on it, built inside your own browser. Nothing you type is uploaded anywhere.
Worked example
These are the figures the calculator opens with and the answer it gives. Change anything above and every number below moves with it.
- Pool shapeRectangle
- Length or diameter32 ft
- Width16 ft
- Shallow end depth3 ft
- Deep end depth6 ft
- Fill rate8 gal/min
- Turnover target8 hours
Water in the pool17,236 gallons
Filling this pool on a garden hose takes 1.5 days of continuous water. Most water utilities sell a bulk fill, and some will not meter a pool fill through the sewer charge if you call first, which is worth more than the hose.
| Surface area | 512 sq ftlength by width |
|---|---|
| Average depth | 4.5 ftmidpoint of shallow and deep |
| Volume | 2,304 cu ft7.48 gallons in each |
| Water weight | 71.9 tons143,741 lb |
| Fill time | 35.9 hoursat 8 gallons a minute |
| Pump for turnover | 35.9 gal/minwhole volume once in 8 hours |
| Heater to raise 10 degrees | 1,437,000 BTU8.34 BTU per gallon per degree |
| Liquid chlorine for a 10 ppm shock | 1.38 gal12.5 percent, sold in gallon jugs, so buy 2 |
| Salt to reach 3,200 ppm | 461 lb12 bags at 40 lb, from zero |
The material list this produces
| Water, gallons | 17,236 |
|---|---|
| Liquid chlorine 12.5 percent, gal | 2 |
| Salt, 40 lb bags | 12 |
| Pump, gal/min | 36 |
What this calculator assumes
- A cubic foot of water is 7.48 gallons and a gallon weighs 8.34 pounds. Those two numbers do all the work on this page.
- Average depth is taken as the midpoint of the shallow and deep ends. That is exact for a pool with one straight slope between them and slightly generous for a pool with a flat shallow shelf and a hopper, which is the safer way for it to be wrong when you are buying chemicals.
- A round pool uses the diameter and ignores the width. An oval is figured as an ellipse, which is length times width times pi over four, not as a rectangle.
- Turnover is the time the pump takes to move the whole volume once. Eight hours is the common residential target and some health codes for public water are stricter, so check yours before you size a commercial pump off this.
- Liquid chlorine trade percent is defined so that one gallon of it raises ten thousand gallons of water by that many parts per million. One gallon of 12.5 percent raises 10,000 gallons by 12.5 ppm, which is where the dose row comes from rather than a chart.
- Salt is figured from zero to 3,200 ppm, which is the middle of the range most chlorine generators want. A pool that already has salt in it needs a test first, because salt only leaves with the water.
Gallons is surface area times average depth
A rectangle 32 by 16 is 512 square feet of surface. A shallow end of 3 feet and a deep end of 6 averages to 4.5, so the pool holds 2,304 cubic feet. There are 7.48 gallons in a cubic foot, which makes it 17,236 gallons.
The average of the two depths is the right number for a pool with a normal sloped floor, where the bottom runs from shallow to deep in a straight line. A pool with a flat shallow shelf and then a sudden diving hopper holds less than the average suggests, so on that shape measure the floor at a few points and use what you get.
Weight follows straight out of gallons at 8.34 pounds each. That 17,236 gallon pool is 143,741 pounds, or 71.9 tons of water sitting on the shell. It is worth knowing before anybody talks about draining a pool in wet ground, because an empty shell in a high water table floats.
A round pool is not a square one
A 24 foot round pool is pi times 12 squared, which is 452.4 square feet. Four feet of flat water over that is 1,809.6 cubic feet and 13,537 gallons. Measure it as 24 by 24 instead and you get 576 square feet, which is 27 percent too much pool.
An oval is the same story. A 30 by 15 oval is pi over 4 times 30 times 15, which is 353.4 square feet, not the 450 a rectangle would give. With a 3 to 5 foot floor that is 10,576 gallons. The overstatement is 27 percent again, because pi over 4 is 0.785 whatever the size.
Twenty seven percent matters on every line under it. On that oval it is the difference between a 22 hour fill and a 28 hour one, between 0.85 gallons of chlorine and 1.08, and between 283 pounds of salt and 360. A shape picked carelessly costs real money in chemicals on day one.
Fill time, pump size and heater
A garden hose runs about 8 gallons a minute at normal pressure. That 17,236 gallon rectangle takes 35.9 hours of continuous water, which is a day and a half, and the calculator says so rather than printing a number nobody reads. Most water companies would rather sell you a tanker than watch that.
Turnover is the whole volume through the filter once in a set number of hours, and eight is the common target. Seventeen thousand gallons in eight hours is 35.9 gallons a minute, which is what sizes the pump. Ask for fewer hours and the pump gets bigger in direct proportion.
Heating is 8.34 BTU for every gallon for every degree. Ten degrees on that pool is 1,437,000 BTU of heat that has to come from somewhere. Spread over a day a 400,000 BTU heater does it in about four hours of run time, and that is before any of it goes back out through the surface overnight.
Chlorine and salt come off a definition, not a chart
Liquid chlorine trade percent is defined so that one gallon of it raises ten thousand gallons of water by that many parts per million. One gallon of 12.5 percent raises 10,000 gallons by 12.5 ppm. So a 10 ppm shock on 17,236 gallons is 1.38 gallons, and since it is sold in gallon jugs you buy 2.
That definition is why this page does not carry a dosing chart. A chart is somebody else's arithmetic on somebody else's pool. The formula behind the row is gallons over ten thousand times the ppm you want over the trade percent you bought, and it works for 10 percent and 12.5 percent alike.
Salt is figured from zero to 3,200 ppm, the middle of the range most chlorine generators ask for, which is 461 pounds or 12 forty pound bags on that rectangle. From zero is the important part. Salt only leaves a pool with the water, so a pool that has been salted before needs a test before anybody buys a bag.
Questions people ask
How many gallons is my pool?
Surface area times average depth times 7.48. A 32 by 16 rectangle with a 3 to 6 foot floor is 512 square feet, 4.5 feet average and 2,304 cubic feet, so 17,236 gallons. A 24 foot round pool with 4 feet of water is 13,537.
How long does it take to fill a pool with a hose?
Divide gallons by the hose flow. At 8 gallons a minute a 17,236 gallon pool takes 35.9 hours, so a day and a half of continuous water. A 13,537 gallon round pool takes 28.2 hours.
What size pump do I need for my pool?
Enough flow to turn the whole volume over once in eight hours. Seventeen thousand gallons in eight hours is 35.9 gallons a minute. Ask for a six hour turnover instead and the flow goes up in the same proportion.
How much liquid chlorine do I need to shock a pool?
One gallon of 12.5 percent raises 10,000 gallons by 12.5 ppm, by definition. A 10 ppm shock on a 17,236 gallon pool is 1.38 gallons, which is 2 jugs. The same pool at 10 percent strength would take 1.72.
Free Contractor Estimate Template, free, no signup, PDF Word and Excel.
Common sizes, worked out
The same calculator with the numbers already filled in, one page per size, each ending in its own material list.