Pool Calculator

Use this pool calculator to find how many gallons or litres your pool holds for any shape, plus square footage, fill time and water cost, and how much chlorine to add to reach your target ppm.

How to Calculate Pool Volume

Every pool volume formula follows the same idea. Find the water surface area, multiply it by the average water depth, then convert cubic feet or cubic meters into gallons or litres.

One cubic foot holds 7.48052 US gallons, because a US gallon is defined as exactly 231 cubic inches. Many pool guides round this to 7.5. That shortcut reads about 0.26% high, which is close enough for a chemical dose but not for a water bill. The pool calculator above uses the full 7.48052.

Rectangle or Square Pool

$$Gallons=L\times W\times D_{avg}\times 7.48$$

L and W are the inside length and width in feet. D_avg is the average water depth in feet. For a flat floor, the average depth is simply the water depth.

Average Depth for a Sloped Floor

$$D_{avg}=\frac{D_{shallow}+D_{deep}}{2}$$

This is exact only when the floor slopes evenly from end to end. Most sport and diving pools have a flat shallow section, a steep break and a deep hopper. Averaging the two end depths overstates the water in those pools.

For a hopper pool, split the floor at the break, where the gentle slope turns steep. Each section gets its own average depth, weighted by how long it is.

$$D_{avg}=\frac{k\times \frac{D_{shallow}+D_{break}}{2}+(L-k)\times \frac{D_{break}+D_{deep}}{2}}{L}$$

Here k is the distance from the shallow end to the break, and D_break is the depth there. This is exact for a rectangular pool. On round, oval and kidney pools, the narrow ends hold less water than their length suggests, so treat the result as an estimate.

The difference is large. Take a 16 × 32 ft pool running from 3.5 ft to 8 ft, with the break 20 ft out at 4.5 ft deep. Its average depth is 4.84 ft, not 5.75 ft, so it holds about 18,550 gallons. A straight average would overstate it by nearly 3,500 gallons. The Pool Slope Calculator helps you work out the floor drop in each section.

Round Pool

$$Gallons=\pi \times r^2\times D_{avg}\times 7.48$$

The radius r is half the diameter. Measure the diameter across the widest point, inside the wall.

Oval Pool

$$Gallons=\pi \times \frac{L}{2}\times \frac{W}{2}\times D_{avg}\times 7.48$$

This treats the oval as a true ellipse. Some pool charts use a single factor of 5.9 instead. That number is just π ÷ 4 × 7.5, so both methods give nearly the same answer.

Above-ground "ovals" with straight sides are different. They are a rectangle with a half circle on each end, so the ellipse formula reads low for them.

$$Area=(L-W)\times W+\pi \times \frac{W^2}{4}$$

A 15 × 30 ft straight-sided oval covers about 401.7 sq ft. The ellipse formula gives 353.4 sq ft for the same label size, about 12% low. Check which shape you have before you dose.

Kidney or Freeform Pool

$$Gallons=0.45\times (A+B)\times L\times D_{avg}\times 7.48$$

A and B are the widths across the two lobes at their widest points. L is the full length. The 0.45 factor is a pool trade estimate, not an exact geometry result, because no two freeform pools share the same curves.

If you need the exact number for a large shock dose or a water bill dispute, use the gallons printed on the builder's plans.

Pool Volume in Litres

$$Litres=L\times W\times D_{avg}\times 1000$$

With all three measurements in meters, each cubic meter holds 1,000 litres. To switch an answer between systems, one US gallon is 3.785 litres. One imperial gallon, still used on some UK and older Canadian pool labels, is 4.546 litres.

Worked Example: 16 × 32 ft Pool, 3.5 ft to 8 ft

1. Surface area = 16 × 32 = 512 sq ft
2. Average depth = (3.5 + 8) ÷ 2 = 5.75 ft
3. Volume = 512 × 5.75 = 2,944 cubic feet
4. Gallons = 2,944 × 7.48052 = 22,023 US gallons
5. Litres = 22,023 × 3.785 = about 83,365 litres

The 7.5 shortcut gives 22,080 gallons for the same pool. That is 57 gallons more than the real figure. If this pool has a steep hopper rather than an even slope, the true volume will be lower still.

How to Measure a Pool

Measurement mistakes cause more wrong answers than formula mistakes. A 6-inch error in depth on a 16 × 32 ft pool changes the volume by about 1,900 gallons.

• Length and width: measure inside wall to inside wall at the waterline, not across the coping or deck.
• Depth: measure from the water surface down to the floor, not from the deck. Take one reading at the shallow end and one at the deep end.
• Round pools: measure the diameter through the center at its widest point.
• Kidney pools: measure the widest point of each lobe (A and B) and the longest straight line end to end.
• Above-ground pools: use the water depth, not the wall height. A 52-inch wall never holds 52 inches of water.

Steps, benches and tanning ledges take up some space. On most backyard pools they cut the total by a few percent, which matters little for a chlorine dose.

Pool Square Footage and Common Pool Sizes

Square footage is the water surface area. It sets your cover size, solar blanket size and how fast the pool loses water to evaporation. To calculate the square foot area of a pool, use only the first part of each volume formula above, before depth enters.

The table below uses the same math as the pool calculator. It shows two average depths, since most backyard pools fall between 4 and 5 ft.

Pool Size	Surface Area (sq ft)	Gallons at 4 ft Avg	Gallons at 5 ft Avg	Litres at 5 ft Avg
12 ft round	113.1	3,384	4,230	16,013
15 ft round	176.7	5,288	6,610	25,020
18 ft round	254.5	7,614	9,518	36,029
24 ft round	452.4	13,536	16,921	64,051
12 × 24 ft rectangle	288	8,618	10,772	40,776
15 × 30 ft rectangle	450	13,465	16,831	63,713
15 × 30 ft ellipse oval	353.4	10,575	13,219	50,040
15 × 30 ft straight-side oval	401.7	12,020	15,025	56,876
16 × 32 ft rectangle	512	15,320	19,150	72,491
18 × 36 ft rectangle	648	19,390	24,237	91,747
20 × 40 ft rectangle	800	23,938	29,922	113,267

A few quick answers come straight from the table. A 24 ft round pool covers about 452 sq ft. A 15 × 30 pool covers 450 sq ft as a rectangle, about 402 sq ft as a straight-sided oval, and about 353 sq ft as a true ellipse. A 20 × 40 pool at 5 ft average depth holds about 113,000 litres, and a 12 × 24 pool holds about 40,800 litres.

Is a 12 ft or 15 ft Pool Big?

No. A 12 ft round pool has about 113 sq ft of water, room for a couple of people to cool off. A 15 ft round pool has about 177 sq ft. Both are small above-ground sizes, and at a typical 4 ft water depth they hold roughly 3,400 and 5,300 gallons.

Is 16 × 32 a Small Pool?

Not really. At 512 sq ft it is a mid-size inground pool. It is big enough for a deep end and short laps, and it is a size you see often in builder catalogs and inground kits.

How Big Is a 200 or 600 sq ft Pool?

A 200 sq ft pool is about 10 × 20 ft. At 5 ft average depth it holds about 7,480 gallons. A 600 sq ft pool is about 20 × 30 ft or 15 × 40 ft and holds about 22,440 gallons at the same depth.

How Big Is a 10,000 or 50,000 Litre Pool?

Work backward by dividing the volume by the depth. A 10,000 litre pool is 10 cubic meters. At 1.2 m deep it covers about 8.3 m², close to a 12 ft round pool filled to 3 ft.

A 50,000 litre pool is 50 cubic meters, or about 13,200 US gallons. At 1.5 m average depth it covers about 33 m², roughly a 12 × 30 ft rectangle.

What Is the Average or Standard Pool Size?

There is no single standard size. Residential inground rectangles commonly run from about 12 × 24 ft to 20 × 40 ft, or roughly 290 to 800 sq ft. Above-ground pools are usually sold by diameter, from about 12 ft to 30 ft round.

Water per Inch, Fill Time and Water Cost

Volume is only the start. The same surface area tells you how much water each inch of level takes, which sizes every top-up and drain.

$$Gallonsperinch=\frac{Are{a}_{sqft}}{12}\times 7.48$$

A 600 sq ft pool needs about 374 gallons for each inch of water. If the level drops 2 inches in a hot week, that is about 750 gallons gone. In metric, each centimeter of depth on 1 m² is 10 litres.

How Long a Pool Takes to Fill

$$Hours=\frac{Gallons}{GPM\times 60}$$

Hose flow varies with water pressure and hose size, so measure yours. Time how long the hose takes to fill a 5-gallon bucket, then use the Gallons Per Minute Calculator to turn that into GPM. For metric hoses, the Liters per Minute Calculator does the same job.

At 9 GPM, a 22,442 gallon pool takes about 41.6 hours. Running two hoses from separate taps can cut that close to half, if your supply pressure holds up.

Pool Calculator Cost: What It Costs to Fill

Water utilities bill either per 1,000 gallons or per CCF. One CCF is 100 cubic feet, which equals about 748 gallons. Read your bill to see which unit your utility uses.

At $1.50 per 1,000 gallons, filling a 22,442 gallon pool costs about $33.66. At $5 per CCF, the same pool costs about $150. If your bill adds sewer charges based on water use, ask your utility whether it offers a pool-fill credit.

Water is heavy, too. Each US gallon weighs about 8.34 lb and each litre about 1 kg, so a 22,442 gallon pool holds roughly 187,000 lb of water. That load is why above-ground pools need firm, level ground.

Pool Calculator for Finance and Loans

Pool loans use the standard fixed-rate payment formula. It is separate from the water math above.

$$M=P\times \frac{r(1+r{)}^n}{(1+r{)}^n-1}$$

P is the amount borrowed, r is the yearly rate divided by 12, and n is the number of monthly payments. A $60,000 loan at 8% for 15 years works out to about $573 per month. Ongoing costs such as water, chemicals and pump power come on top of that payment.

How Much Chlorine to Add to a Pool

Chlorine dosing starts from one fact: 1 ppm means 1 milligram per litre. Once you know your volume in litres, the amount of active chlorine follows directly.

$$C{l}_{grams}=\Delta F{C}_{ppm}\times \frac{Volum{e}_{litres}}{1000}$$

$$Product=\frac{C{l}_{grams}}{Strength}$$

For a solid product, strength is the available chlorine percent on the label as a decimal, such as 0.65. For liquid chlorine, the percent is a "trade percent", meaning grams per 100 mL. So 12.5% liquid chlorine carries 125 grams of available chlorine in each litre.

How Much Is 1 ppm of Chlorine?

In 10,000 US gallons, 1 ppm is 37.85 grams of available chlorine. In 10,000 litres it is exactly 10 grams. The table turns that into product amounts.

Chlorine Product	Per 1 ppm in 10,000 US gal	Per 1 ppm in 10,000 L	Side Effect per 1 ppm FC
Liquid chlorine 12.5%	10.24 fl oz	80 mL	About 1.65 ppm salt
Liquid chlorine 10%	12.8 fl oz	100 mL	About 1.65 ppm salt
Household bleach 8.25%	15.5 fl oz	121 mL	About 1.65 ppm salt
Household bleach 6%	21.3 fl oz	167 mL	About 1.65 ppm salt
Cal-hypo 65%	2.05 oz	15.4 g	About 0.7 ppm calcium hardness
Cal-hypo 73%	1.83 oz	13.7 g	About 0.7 ppm calcium hardness
Dichlor 56%	2.38 oz	17.9 g	About 0.9 ppm CYA
Trichlor 90%	1.48 oz	11.1 g	About 0.6 ppm CYA

The last column is the part most dose charts leave out. Every product leaves something behind. Daily trichlor tablets slowly push CYA up, and cal-hypo slowly raises calcium hardness. That buildup, not the chlorine itself, is what eventually forces a partial drain.

Liquid chlorine loses strength in storage, faster in heat and sunlight. A jug that sat through a summer may test well below its label, so your real dose can run higher than the math says.

How Much Chlorine for a 1,000 Litre Pool?

Each 1 ppm needs 1 gram of available chlorine. That is 8 mL of 12.5% liquid chlorine or about 1.5 g of 65% cal-hypo. To raise a fresh fill from 0 to 3 ppm, add about 24 mL of 12.5% liquid chlorine.

How Much Chlorine Do I Need for 10,000 Litres?

Each 1 ppm needs 10 grams of available chlorine. That is 80 mL of 12.5% liquid chlorine or 15.4 g of 65% cal-hypo. Raising free chlorine from 2 to 4 ppm takes 160 mL of liquid chlorine.

How Much Chlorine to Shock a 40,000 Litre Pool?

It depends on your stabilizer (CYA) reading, because the shock level rises with CYA. A widely used guide from Trouble Free Pool sets shock at about 40% of the CYA level.

With 40 ppm CYA, the shock target is 16 ppm. From a current 2 ppm, you need a 14 ppm rise. In 40,000 litres that is 560 grams of available chlorine, or about 4.5 litres of 12.5% liquid chlorine. Using 65% cal-hypo, it is about 860 grams.

Free Chlorine, Stabilizer and Safe Levels

What Is Free Chlorine in a Pool?

Free chlorine (FC) is the chlorine still available to kill germs and algae. Combined chlorine is chlorine that has already reacted with sweat, urine and other nitrogen waste. It causes the "chlorine smell" people blame on too much chlorine.

Total chlorine is the two added together. Subtract FC from total chlorine to get combined chlorine.

What Is the Ideal Chlorine Level for a Pool?

For a pool with no stabilizer, 1 to 4 ppm is the long-standing range. Once CYA is in the water, that range stops working on its own. CYA holds most of the chlorine in reserve, so the same FC reading kills far more slowly at 80 ppm CYA than at 30 ppm.

That is why the CDC's Model Aquatic Health Code (MAHC) treats a CYA to free chlorine ratio above 45 to 1 as an imminent health hazard, a rule added in the 4th edition. The home-pool guide from Trouble Free Pool is stricter. Its minimum works out to about 7.5% of CYA, and its chart rounds that up to whole numbers, such as 4 ppm at 50 CYA and 8 ppm at 100 CYA.

CYA (ppm)	MAHC Hazard Below (FC ppm)	Home Minimum, 7.5% of CYA	Shock Level, 40% of CYA
30	0.67	2.25	12
40	0.89	3	16
50	1.11	3.75	20
60	1.33	4.5	24
80	1.78	6	32
100	2.22	7.5	40

Read across a row and the problem with high CYA is clear. At 100 ppm CYA, a 4 ppm reading that looks "ideal" is barely half the home minimum. Lowering CYA takes a partial drain and refill, since no common chemical removes it.

Can I Swim in 5 ppm Chlorine?

Yes. The 5th edition of the MAHC names free chlorine above 10 ppm while swimmers are in the water as the closure point. At 5 ppm you are well below that, and with normal CYA levels 5 ppm is often the right everyday target.

Does Shock Increase Free Chlorine?

Chlorine shock does. Cal-hypo, dichlor and liquid chlorine all raise FC by the amounts in the dose table. Non-chlorine shock (potassium monopersulfate) oxidizes waste but adds no free chlorine at all.

Can I Shock My Pool 2 Days in a Row?

Yes. Clearing algae often means holding the shock level for several days, retesting and topping up as it falls. The process is usually done when the water is clear, combined chlorine is 0.5 ppm or less, and FC drops 1 ppm or less overnight.

How to Raise Chlorine Level in a Pool Quickly

Use a fast-dissolving product: liquid chlorine or cal-hypo. Add it with the pump running, pour liquid chlorine in front of a return jet, and retest after about 30 minutes of circulation. Trichlor tablets are too slow for this; they are meant for steady daily feeding.

What Destroys or Lowers Chlorine in a Pool?

Sunlight is the biggest drain. UV light breaks chlorine down within hours in a pool with no CYA. Swimmer waste, leaves, pollen and warm water all use chlorine up faster too.

To lower a high reading quickly, stop adding chlorine, remove the cover and let the sun work. A chlorine neutralizer such as sodium thiosulfate acts within minutes, but dose it by the label in small steps, since it is easy to overshoot to zero.

How Long Can a Pool Go Without Chlorine?

Not long. Once FC hits zero, nothing is stopping bacteria and algae. In warm, sunny weather an outdoor pool can turn cloudy or green within a few days. Plan for someone to test and dose while you travel, or use a feeder with tablets.

pH, Alkalinity and the Order to Adjust Them

pH and alkalinity are not the same thing. pH measures how acidic or basic the water is right now. Total alkalinity (TA) measures the buffer that resists pH change, in ppm. High TA makes pH drift upward, and low TA lets pH swing.

Is 7.8 pH Too High for a Pool?

It is the top of the acceptable range, not past it. The MAHC 4th edition range is 7.0 to 7.8, and many pool owners aim for 7.4 to 7.6. At 7.8, chlorine works more slowly in a pool without stabilizer, so bring it down soon.

A pH of 9.5 is far too high for pool water. Chlorine is weak at that level, scale forms quickly on surfaces and heaters, and swimmers' eyes will sting.

Can I Add Chlorine if pH Is High?

Yes, and if FC is near zero you should. High pH does not stop chlorine from working. It shifts more of it into the slower-acting hypochlorite form, as the table shows for water with no CYA at 77°F.

pH	Active Hypochlorous Acid (approx.)
7.0	78%
7.2	69%
7.4	58%
7.6	47%
7.8	35%
8.0	26%

In a stabilized outdoor pool, CYA holds most chlorine in reserve anyway, so pH has a much smaller effect on killing power. Lower the pH after the chlorine is in, mainly to protect surfaces and comfort.

Is 40 or 80 Alkalinity Good for a Pool?

Pool test strips often show alkalinity as a number that people read as a percent, but it is ppm. Most pool guides target about 80 to 120 ppm. So 80 ppm is fine, sitting at the low end of normal. At 40 ppm the buffer is too weak and pH will bounce around.

Baking soda raises TA with only a small pH rise. In 10,000 gallons, about 1.4 lb raises TA by 10 ppm. The pool calculator shows this amount for your own volume.

What Lowers or Raises Pool pH Quickly?

• To lower pH: muriatic acid or sodium bisulfate (dry acid). Both also lower TA a little.
• To raise pH: soda ash (sodium carbonate) works fastest. Aeration from fountains or jets aimed upward also raises pH, without adding to TA.

Does Shock Increase pH?

Some types do. Cal-hypo and liquid chlorine are strongly alkaline and push pH up when added. Much of the liquid chlorine rise reverses as the chlorine is used up. Dichlor is close to neutral, and trichlor is acidic, so it pulls pH down over time.

Do I Adjust Alkalinity, pH or Chlorine First?

Test everything first, then adjust in this order:

1. Total alkalinity, because it controls how pH behaves.
2. pH, once the buffer is right.
3. Calcium hardness and CYA, which change slowly and need retesting after a day or two.
4. Chlorine, dosed to the level your CYA reading calls for.

One exception overrides the order. If free chlorine is near zero, add chlorine first. Sanitizing the water cannot wait for the balance work.

Pool Calculator FAQs

How many gallons is my pool?

Multiply surface area in sq ft by average depth in ft, then by 7.48. For a quick mental estimate, a rectangle 15 × 30 ft at 5 ft average holds about 16,800 gallons. Enter your own sizes in the pool calculator for an exact figure in gallons, litres, cubic meters or imperial gallons.

Is there a pool calculator app?

You don't need one. This pool calculator runs online in any phone browser and keeps working poolside. Save the page to your home screen and it opens like an app.

How is pool volume different from pond or tank volume?

The geometry is the same, but ponds have sloped, uneven sides and tanks often have cone or dished ends. Use the Pond Calculator for garden ponds and the Tank Volume Calculator for storage tanks.

Does the water in the pipes and filter count?

Only slightly. Schedule 40 2-inch pipe holds about 1.7 gallons per 10 ft, which is tiny next to a pool. You can check a specific run with the Pipe Volume Calculator. To size the pump that moves that water, see the Pump Pressure Calculator.