Pool Volume Calculator

How to use the pool volume calculator

This pool volume calculator, a pool gallons calculator and pool water calculator in one, answers the question every pool owner meets sooner or later: how many gallons are in my pool? You need the number to dose chemicals, size a pump, filter or heater, and estimate the water bill for a fill. It works for in-ground and above-ground pools, hot tubs and spas, and it shows its working so you can check every figure.

1. Measure the water. Measure the length and width of the water surface inside the walls, or the diameter of a round pool, with a tape measure.
2. Measure the depth. Measure the depth at the shallow end and at the deep end, and where the floor starts and stops sloping if it has a break point. Note whether you measured from the water surface or from the top of the wall.
3. Choose the shape. Pick Pool or Hot tub or spa, then the shape. Use Freeform with an average length and width, or Surface area known, for an irregular pool.
4. Enter the sizes. Type each measurement in the unit you chose under Measure in, or with its own unit, such as 4' 6", 54 in or 1.4 m.
5. Pick the floor. Choose Same depth throughout, Shallow end and deep end, or Sloped floor with a break point, and fill in the depths.
6. Read the volume. The results show the volume in US gallons, imperial gallons, liters, cubic meters and cubic feet, with the surface area, the average depth and the weight of the water. Copy them, download a CSV file or print them.

Three more tabs take the volume further. Fill time & cost works out how long a hose or a delivery takes and what the water costs at your rate. Pump & turnover gives the pump flow that moves the whole pool through the filter in a chosen time. Chemical dose does the arithmetic for raising free chlorine, bromine, salt or stabilizer by a number of parts per million, from the strength printed on your own product.

How to calculate pool volume

Pool volume is the surface area of the water times its average depth. Work in feet to get cubic feet, then convert to gallons. A U.S. gallon is defined as exactly 231 cubic inches and a cubic foot is 1,728 cubic inches, so a cubic foot holds 1,728 ÷ 231 = 7.48052 gallons:

volume (cubic feet) = surface area (sq ft) × average depth (ft)
gallons             = cubic feet × 7.48052
liters              = cubic feet × 28.3168

For a rectangular pool 32 ft long and 16 ft wide that is 3 ft 6 in deep at the shallow end and 6 ft 6 in at the deep end, with an even slope between them, the surface area is 32 × 16 = 512 sq ft and the average depth is (3.5 + 6.5) ÷ 2 = 5 ft. The volume is 512 × 5 = 2,560 cubic feet, which is 19,150.13 gallons or 72,491.13 liters. That is the calculator's starting example.

You may have seen the shortcut "length × width × average depth × 7.5". The 7.5 is 7.48052 rounded up, so it overstates every rectangular pool by about 0.26%. For round pools the shortcut "diameter × diameter × depth × 5.9" folds in π ÷ 4; the exact figure is 7.48052 × π ÷ 4 = 5.875, so 5.9 overstates by about 0.42%. The calculator uses the exact factors and rounds only what it displays.

Pool volume formulas by shape

Each shape in the calculator uses one of these surface area formulas, and the letters match the labels on the drawings in the tool. Multiply the area by the average depth for the volume. The examples are the calculator's starting sizes, all at a constant 5 ft depth except the hot tub octagon.

Two kinds of oval are in the list because pools come in both. A true ellipse curves all the way round. Most above-ground ovals, and many in-ground ones, have two straight sides joined by half circles at the ends; with the same overall length and width that shape holds more water, 15,025.17 instead of 13,219.17 gallons in the example. Check the sides of your pool before you choose.

Kidney and freeform pools have no exact formula. The kidney rule, 0.45 × (A + B) × L, is a widely used rule of thumb rather than geometry, and other published rules use slightly different factors. For a freeform pool, measure the length in three or four places and the width in several places across, and average each set. Where accuracy matters, for example for a large dose or a heater, use the surface area from the pool's plans with Surface area known, or split the pool into shapes you can measure and add their volumes.

Average depth and sloped floors

The depth is where most volume mistakes come from. The calculator offers three floors:

• Same depth throughout. Above-ground pools, hot tubs and many plunge pools. The volume is area × depth.
• Shallow end and deep end. A floor that slopes evenly from one end wall to the other. The average depth is exactly (shallow + deep) ÷ 2, so a pool 3 ft 6 in to 6 ft 6 in deep averages 5 ft. For a rectangle, an ellipse or a round-ended oval the volume is exactly area × that average, because the shape is the same at both ends.
• Sloped floor with a break point. The usual sport or diving profile: a flat shallow area, a steeper slope at the break point, then a flat deep end. Enter the shallow depth S, the deep depth D, the length of the flat shallow part a and the length of the slope b. The rest of the length is deep end.

Averaging the two end depths is a poor guide for a break-point floor. Take a 40 × 20 ft pool that is 3 ft 6 in deep for its first 20 ft, slopes over the next 8 ft, and is 8 ft deep for the last 12 ft. The real volume is 4,240 cubic feet, 31,717.4 gallons, an average depth of 5.3 ft. Averaging 3.5 and 8 gives 5.75 ft and 34,410.39 gallons, about 8.5% too much water.

For round, oval, octagonal and L-shaped pools the width changes along the length, so the narrow ends hold less of the deep water. The calculator does not average here: it adds up width × depth slice by slice along the whole length, exactly, using the straight and curved edges of the outline. For kidney, freeform and known-area pools, which have no exact outline, it uses area × the average depth along the length and labels the result as an approximation.

Water level below the top. Pools are rarely filled to the brim. If you measured the depth from the top of the wall or the coping, choose The top of the wall and enter how far below it the water sits; the calculator takes that off every depth. An 18 ft round above-ground pool with 52 in walls holds 8,248.76 gallons filled to the top, but 7,296.98 gallons with the water 6 in below it.

Worked examples

A 16 × 32 ft in-ground pool

A rectangle 16 ft wide and 32 ft long, 3 ft deep at the shallow end and 8 ft at the deep end with an even slope, averages 5.5 ft deep. Its surface area is 512 sq ft, its volume 2,816 cubic feet, which is 21,065.14 gallons or 79.74 m³.

A kidney pool

A kidney pool 30 ft long, 10 ft across the small lobe and 14 ft across the large one, 3 ft 6 in to 6 ft 6 in deep: the rule of thumb gives 0.45 × (10 + 14) × 30 = 324 sq ft, and at a 5 ft average depth about 12,118 gallons. Treat the last few hundred gallons as uncertain: the kidney factor is an approximation.

An L-shaped pool with a shallow wading area

An L-shaped pool 40 ft long and 20 ft wide overall, with a 12 × 8 ft corner missing at the deep end, a flat 3 ft 6 in shallow end for 16 ft, a 10 ft slope and an 8 ft deep end. Its surface area is 704 sq ft and it holds 27,992.1 gallons. If the missing corner were at the shallow end instead, the same outline would hold 31,223.69 gallons, because the deep end would be the full width.

Metric: a 10 × 5 m pool

A 10 m by 5 m pool, 1.2 m deep at one end and 2 m at the other, has a surface area of 50 m² and an average depth of 1.6 m, so it holds 80 m³, which is 80,000 liters or 21,134 US gallons. Choose Meters under Measure in and Liters under Volume in to work in metric throughout.

The volume is also the place to start for anything dug or delivered by the yard, such as sand for an above-ground pool base: the cubic yard calculator turns an area and a depth into cubic yards, and the square footage calculator works out the area of a deck or patio around the pool.

Gallons, liters and cubic feet

Every conversion here is exact by definition. NIST Handbook 44 defines the U.S. gallon as 231 cubic inches (exactly), and since an inch is exactly 2.54 cm, a gallon is exactly 3.785411784 liters. The imperial (U.K.) gallon is a different unit, exactly 4.54609 liters according to NIST Special Publication 811, about 20% larger than the U.S. gallon.

So to turn gallons into liters, multiply by 3.785411784; to turn liters into gallons, divide by it. A cubic meter is 1,000 liters, and 100 cubic feet, the unit many U.S. water bills use, is 748.05 gallons. Here are some pool sizes in both:

Above-ground pool volume

Above-ground pools have a flat floor, so their volume is the surface area times the water depth. Use Round or Oval with straight sides, Same depth throughout, and either the water depth itself or the wall height with the gap to the water. This table assumes 48 in of water:

A pool's nominal size may be measured outside the wall, and the walls, top rails and liner take up a little room, so measure the water itself if you can. The water is heavy, too: at about 8.35 lb per gallon, a 24 ft round pool with 48 in of water holds about 112,967 lb of it, which is why above-ground pools go on firm, level ground and not on a deck unless a structural engineer confirms the deck can carry it.

Hot tub and spa volume

Choose Hot tub or spa at the top of the tool. The shapes change to square or rectangle, round and octagon, the floor is a single water depth, and the calculator keeps the hot tub's sizes apart from the pool's, so you can switch back and forth. A 7 × 7 ft hot tub with 3 ft of water has an outline volume of 1,099.64 gallons, 4,163 liters; a round one 7 ft across holds 863.65 gallons.

Molded seats, steps and footwells take up part of a hot tub's outline, so it holds less water than the outline volume. If the owner's manual states a capacity, use that figure for chemicals. Otherwise measure the water you add: fill from empty through a meter, or time the fill with the bucket test on the Fill time & cost tab. CDC's minimum free chlorine for hot tubs is higher than for pools; see the chemistry section below.

How long it takes to fill a pool, and what it costs

Fill time is the volume divided by the flow rate. Hoses and taps vary too much for any one figure to be useful, so measure yours: time how long the hose takes to fill a bucket of known size. If a 5-gallon bucket fills in 30 seconds, the flow is 10 gallons per minute, and the example pool's 19,150 gallons take 31 h 55 min. Two hoses on separate taps can roughly halve that, if the supply keeps up.

fill time (minutes) = gallons ÷ flow (gallons per minute)
water cost          = gallons ÷ 1,000 × price per 1,000 gallons
                    = cubic feet ÷ 100 × price per CCF

The cost comes from your water bill. U.S. utilities quote rates per 1,000 gallons, or per 100 cubic feet (CCF, 748.05 gallons), and elsewhere per cubic meter. At an example rate of $5.00 per 1,000 gallons, filling the example pool costs $95.75. Many bills also charge for sewer on the water you use, and some utilities treat a pool fill differently; ask yours. Delivered water is priced per load, so divide the volume by the truck's capacity.

Topping up is the same arithmetic: raising the level of the 32 × 16 ft example by 1 in takes 319.17 gallons. Choose Raise the level on the tab to use your pool's surface area.

Pump size and turnover

A turnover is the time the pump takes to move a volume of water equal to the whole pool through the filter. The flow it needs is the volume divided by the time:

pump flow (gpm) = gallons ÷ (turnover hours × 60)

For the 19,150-gallon example pool, an 8-hour turnover needs 39.9 gallons per minute (151.02 L/min), a 6-hour turnover 53.19 gpm and a 12-hour turnover 26.6 gpm. The other way round, a pump that really moves 50 gpm turns that pool over every 6 h 23 min.

Two cautions. A pump's label flow is measured against little resistance; in a real system with pipes, fittings, a filter and a heater it moves less, so read the flow at your system's resistance from the pump's performance curve or a flow meter. And the filter has to be rated for the flow you choose. Public pools must meet the turnover times in their local health code, many of which are based on CDC's Model Aquatic Health Code; for a home pool, the pump and filter manuals are the place to look.

Pool chemicals: dose arithmetic and CDC ranges

Chemical doses scale with volume, which is why an accurate volume matters. The Chemical dose tab only does the arithmetic. It does not know your product, and it is not a substitute for the label. Pool and spa sanitizers are sold under a U.S. EPA pesticide registration, and as the EPA's guide to pesticide labels puts it, the label is the law: follow its directions, its limits and its safety instructions.

In pool water, 1 part per million (ppm) is 1 milligram per liter; the USGS notes the two are generally equivalent below about 7,000 mg/L of dissolved solids. So the amount of an ingredient the water needs is:

ingredient (grams) = ppm change × liters of water ÷ 1,000
product            = ingredient ÷ (strength % ÷ 100)
                     (grams for % by weight, milliliters for % weight per volume)

For example, raising free chlorine by 1 ppm in 10,000 gallons (37,854.12 liters) needs 37.85 g of available chlorine. From a liquid labeled 12.5% weight per volume that is 302.83 mL, about 10.24 fl oz; from a granular product at 65% by weight, 58.24 g, about 2.05 oz. These strengths are examples, not recommendations. Raising salt by 1,000 ppm in the same water takes 37.85 kg (83.45 lb) of pure salt.

Use the strength of the ingredient your test measures. Free chlorine is reported as available chlorine, so use the available chlorine figure, not the percentage of the active ingredient, if the label lists both. A liquid whose strength is given by weight needs its specific gravity, from the label or the safety data sheet, to turn weight into volume. The tool does not work out pH, alkalinity or calcium adjustments: how far pH moves depends on the water's alkalinity, so there is no simple proportion, and the product label is the guide.

The ranges CDC gives for healthy swimming, from its pages on home pool and hot tub water treatment and keeping your pool safe:

Safety, from CDC's pool chemical safety guidance: pool chemicals can injure people when they are mixed together, so never mix them with each other, keep incompatible products apart in their original labeled containers, wear the protective equipment the label calls for, and keep chemicals secure and away from children and pets. Beyond that, a cautious habit: add part of a dose, let the pump mix it in, and test again before adding more.

How we calculate

The tool and every example on this page use the same code, and the examples are checked against it automatically.

• One internal unit. Every length is converted to feet as you type it, using 1 ft = 0.3048 m exactly and 1 ft = 12 in. Volumes are worked out in cubic feet and converted once, at the end, with exact factors: 1 gallon = 231 cubic inches, 1 imperial gallon = 4.54609 liters, 1 cubic foot = 28.316846592 liters.
• Exact geometry where the outline is known. For rectangles, round pools, ellipses, round-ended ovals, octagons and L-shapes, the volume is width × depth added up along the length, worked out in closed form for straight and circular edges, so a sloped floor in a round pool is exact rather than averaged.
• Labeled approximations. Kidney pools use the 0.45 × (A + B) × L rule of thumb and freeform pools average length × average width; both are marked as approximations.
• Depths. Constant, an even slope (average of the two ends), or a flat shallow part, a slope and a flat deep end. The gap between the top of the wall and the water is taken off every depth.
• Rounding. Results are rounded only for display, to two decimals; money to the cent; times to the minute.
• Not included: steps, benches, seats, a spa spillover or a sump, and the slight curve where the floor meets the walls. Add or subtract them yourself if they are large. Water weight assumes 1 kg per liter; warm pool water is a fraction of a percent lighter, according to the USGS water density table.

Your measurements stay on your device

• Nothing is uploaded. Every calculation runs as JavaScript in your browser tab. The page's Content-Security-Policy only allows connections back to this site, and the tool makes none: open your browser's developer tools, choose the Network tab and type a few numbers, and no request appears.
• It keeps working offline. Once the page has loaded, you can disconnect and keep calculating.
• No account, no cookies. The tool remembers your pool, hot tub, units and last tab in your browser's local storage, on your device only.

Sources

• NIST Handbook 44 (2026), Appendix C: General Tables of Units of Measurement, from the current edition (the U.S. gallon, 231 cubic inches exactly; 3.785411784 liters).
• NIST Special Publication 811, Guide to the SI, Appendix B.8: Factors for units listed alphabetically (the imperial gallon, 4.54609 liters exactly).
• Centers for Disease Control and Prevention (CDC): Home Pool and Hot Tub Water Treatment and Testing.
• CDC: Guidelines for Keeping Your Pool Safe and Healthy.
• CDC: Pool Chemical Safety.
• U.S. Environmental Protection Agency: Introduction to Pesticide Labels.
• U.S. Geological Survey (USGS): Brackish Groundwater Assessment (milligrams per liter and parts per million).
• USGS Water Science School: Water Density.

Reviewed by microplugins · Last updated October 2026

This is an educational tool, not professional, health or safety advice. Results are the volume of the shape and depths you enter; steps, seats and other features change the real figure. For chemicals, the product label's directions come first, and public pools follow their local health code. Example rates, flows and strengths are illustrations, not recommendations or market prices.