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Pool Volume Calculator
Use this free pool volume calculator to find out how much water your pool holds in gallons, liters, and cubic feet. Pick your pool shape — rectangular, round, or oval — enter the size and the average depth, and the calculator works out the volume right away. Knowing the volume is the first step to dosing chemicals correctly, sizing a pump and filter, and figuring out how much water a fill or a refill will take.
How it works
Pool volume is just surface area times average depth. First the calculator finds the surface area of the water from the shape you pick, then it multiplies that area by the average depth to get the volume in cubic feet, and finally it converts cubic feet into gallons and liters. The shape matters because a round pool holds less water than a rectangular pool with the same length and width — the corners are missing, so the area is smaller.
For a rectangular pool, the surface area is length times width. For a round pool, it is pi times the radius squared, where the radius is half the diameter. For an oval pool, it is pi times half the length times half the width. Once the area is known, the rest of the math is the same for every shape: area times average depth gives cubic feet, and one cubic foot of water is 7.48 gallons, or about 28.32 liters.
The trickiest input is the average depth, because very few pools have a flat bottom. Most in-ground pools slope from a shallow end down to a deep end, so no single depth reading describes the whole pool. The standard fix is to measure the depth at the shallow end and at the deep end, add them together, and divide by two. That average is accurate enough for chemical dosing and equipment sizing as long as the slope is fairly even. If your pool has a flat bottom, or it is an above-ground pool, the average depth is simply the depth of the water.
Measure the water depth, not the wall height. The water in a pool normally sits a few inches below the top edge, and the wall height above the water holds no water at all. Measuring from the deck to the floor overstates the depth and inflates the volume, which leads to overdosing chemicals. For above-ground pools this matters a lot: a pool with 52-inch walls often holds only about 48 inches of water. Use a tape measure from the water surface straight down to the floor at each end.
Round and oval pools need one extra care point. For a round pool, measure straight across the middle through the center — that is the diameter — and do not measure along the edge, which gives a shorter chord and understates the size. For an oval pool, measure the longest straight run for the length and the widest point across the middle for the width. If the pool has steps, a sun shelf, or a bench built into one corner, those features displace a little water, but for most home pools the difference is small enough to ignore.
The result is useful in three everyday jobs. First, chemical dosing: chlorine, shock, pH increaser and decreaser, alkalinity adjusters, and algaecide are all dosed per 10,000 gallons, so a pool you think holds 15,000 gallons but really holds 20,000 will stay under-dosed and turn green. Second, equipment sizing: pumps are rated in gallons per minute and filters in gallons per hour, and the turnover rate — how long it takes to filter the whole pool once — comes straight from the volume. Third, water bills and fill time: knowing the gallons tells you what a full refill costs and how long the hose needs to run.
Keep in mind that the volume this calculator gives is the volume of water, not the volume of the pool shell. It also assumes the pool is filled to its normal operating level. If you drain the pool partway for winter or for repairs, the water in it is less, and the chemical dose should be based on the water that is actually there. When in doubt, round the volume slightly up for equipment sizing and use the exact figure for chemicals.
Worked example
A rectangular in-ground pool measures 20 feet long and 10 feet wide. The shallow end is 3 feet deep and the deep end is 7 feet deep.
Step 1: Find the average depth — (3 + 7) ÷ 2 = 5 feet.
Step 2: Find the surface area — 20 × 10 = 200 square feet.
Step 3: Find the volume in cubic feet — 200 × 5 = 1,000 cubic feet.
Step 4: Convert to gallons — 1,000 × 7.48 = 7,480 gallons.
Step 5: Convert to liters — 1,000 × 28.3168 = 28,317 liters.
The pool holds 1,000 cubic feet of water, which is 7,480 gallons or about 28,317 liters. A standard chlorine dose written for 10,000 gallons would need about three-quarters of the listed amount for this pool, and a pump rated at 40 gallons per minute would turn the whole pool over in about 3 hours and 7 minutes.
FAQ
How do I find the average depth of my pool?
Measure the depth at the shallow end and at the deep end, add the two numbers together, and divide by two. For example, a pool that is 3 feet deep at the shallow end and 8 feet deep at the deep end has an average depth of 5.5 feet. If your pool has a flat bottom, the average depth is just the depth everywhere.
How many gallons are in a cubic foot of water?
One cubic foot of water holds 7.48 gallons. To convert any pool volume from cubic feet to gallons, multiply the cubic feet by 7.48. One cubic foot is also about 28.32 liters.
Why do I need to know my pool volume?
Pool volume controls almost everything about pool care. Chemical doses for chlorine, pH adjusters, and algaecide are all based on gallons, and pump and filter sizes are chosen from the volume too. Guessing the volume usually means adding too much or too little chemical.
Does this calculator work for above-ground pools?
Yes. Above-ground pools are usually round or oval with a flat bottom, so the average depth is just the water depth. Measure the water depth, not the wall height, because the water normally sits a few inches below the top of the wall.