How to Calculate Your Pool Size—And Nail Maintenance Costs

It’s one of the inevitabilities in our world. The sun always rises, the winter always comes, and at a certain point, every pool owner who has put off determining the size of their pool caves in. And it’s for a good reason: basically anything you do to your pool is based on its volume, or how much water it contains. You wouldn’t add the same amount of creamer to your coffee if it was in an espresso cup or an oversized thermos, would you?

Of course, I can’t promise that we aren’t going to have to channel a bit of middle school algebra, but I can promise you that it’s not as complicated as it sounds. First, I’ll show you how to calculate your pool volume without crunching any numbers, and then I’ll help you calculate a more specific pool volume based on the shape of your pool. Hey, we’ll get through this together.

Seriously, The Size of Your Pool Matters 

Alright, I’m not just going to tell you that everything is based on water volume. That’s probably not true. But it certainly does seem like almost everything you do to your pool is based on its size. The type of pool pump that you should get, the amount of chemicals you should use, how long you run your circulation system everyday... all of these foundational aspects of everyday pool operations depend on how much water your equipment is expected to move and your chemicals are expected to treat. So whether or not you’re dreading the calculations to come, I can tell you they’re totally worth it—and should save you a chunk of cash in maintenance costs.

Come On, Let’s Be Measured About This

Unfortunately, I can’t be in your backyard with a measuring tape. Really wish I could help out, but it’s just not possible. So before we go further—even in this next step, where you won’t need to crunch any numbers to find out how much water is in your pool—you have got to know what you’re working with. And the type of measurements you need? Those will depend on what shape of pool you have.

For a rectangular pool, you’ll want to know how long, wide, and deep your pool is. Remember to measure both the shallow end and the deep end.

For a circular pool, you just need to measure across the middle, and measure how deep it is.

Note: To keep your calculations as straightforward as possible later, it’s best to round to the nearest foot. Don’t worry, your calculation will be accurate enough for choosing a pump, adding chemicals to your water, and all that other fun stuff pool owners get to do. And if you are just going to use the charts in the next step, no need to measure your depth.

how to calculate your pool size

Knowing your pool size will save you a lot of money on your pump and your energy bill, but it’ll also help you find the perfect heat pump, like the Energy-Saving ComforTemp Pool Heat Pump 65,000 BTU to heat 13,000 Gallons. According to customer Steve, “Simple install and simple set up. Heated my pool from 66 to 82 degrees in about 2 complete days.”

Calculate Your Pool Volume—Without Math 

So you’re really not into algebra, huh? That’s totally okay. Just find the size of your pool on one of these charts, and you’ll find the average gallons for that pool. Since not all pools have the standard depth, these numbers are not exact—but approximate. But hey, if you just came here to get a general sense of how many thousands of gallons your in-ground or above-ground pool contains, just check out these charts and you’re off scot-free.

how to calculate your pool size

how to calculate your pool size

Calculating by Pool Shape

Got your measurements and your calculator ready? This is where it gets fun. Or, you know, fulfilling. These might look like equations (well, okay, they are), but they couldn’t be more straightforward. Read on and you’ll see exactly what I mean. 

Rectangle-Shaped Pools 

This is your standard, inground pool type—but that doesn’t mean they’re all the same. You’ll need to calculate your volume for a rectangular or square pool based on whether the bottom of your pool is flat and has one depth, is sloped and has a gradual depth, or has two flat depths with a single drop off. Remember, this is the technical part!

Want a pump that adjusts for your pool’s specific size and saves you a ton of money to boot? The Blue Torrent 2 HP Variable-Speed Pump is ultra-powerful, comes with a lifetime warranty, eligible for rebates, and pays itself off in under a year by energy saved. As customer Bill Britton says, “Runs great. Super quiet.”

Constant Depth

If your pool floor is flat, you get the simplest equation of all. The volume of your pool will be the length multiplied by the width and depth, with all units in feet:

Volume = Length x Width x Depth

But remember, we want gallons—not feet. Since one cubic foot of water contains 7.5 gallons, you’ll want to multiply your volume in feet by 7.5 to get your volume in gallons.

So if you have a pool that is 28 feet long, 14 feet wide, and 5 feet deep, your calculation would be:

(28 x 14 x 5) x 7.5 = 14,700 gallons.

Gradually Depth with a Sloped Floor

If your pool floor has a shallow end, a deep end, and a sloped floor between the two, you’ll need to find your average depth first. To find your average depth, just add the depth of your shallow end and the depth of your deep end and divide that number by two:

(Depth of Pool’s Shallow End + Depth of Pool’s Deep End)/2 = Average Depth

Once you have the average depth, you’re ready to calculate your pool’s volume by multiplying length by the width and depth, with all units in feet:

Volume = Length x Width x Depth

Again, you’ll want to then convert your volume from feet to gallons by multiplying it by 7.5.

So if you have a pool that is 32 feet long, 16 feet wide, and with a constant depth of 5 feet, your calculation would be:

(32 x 16 x 5) x 7.5 = 19,200 gallons.

It’s not just the amount of gallons in your pool that matters—it’s also how many sit on top of your pool cover in the winter. Keep your cover light and secure with the BLACK+DECKER 800 GPH Automatic Pool Cover Pump, which detects up to a quarter inch of rain and works on its own—fast.

how to calculate your pool size

Two Different Depths with a Drop Off

If your pool has a drop off that separates two constant depths, it’s best to treat them as separate pools. Go ahead and use the calculation above for constant depth twice, one for each depth, and then add the two totals together to know your combined gallons. I know, double the work. But hey, you’ve got a pretty cool pool!

Circle-Shaped Pools

This one most commonly applies to above-ground pools. This is an equation that is far from complicated, but we’ll first need to figure out the radius of your pool. To do this, you’ll just need to half your width, or divide it by two:

Radius = Width/2

Once you have your radius, you’re ready to calculate your pool’s volume by multiplying 3.14 by your radius times your radius and then by your depth, with all values in feet:

Volume = 3.14 x (Radius x Radius) x Depth

Again, you’ll want to then convert your volume from feet to gallons by multiplying it by 7.5.

So if your pool has a width of 18 feet and a depth of 5 feet, you’d first calculate your radius to be 9. Then you’d plug in the following:

Volume = [3.14 x (9 x 9) x 5] x 7.5= 9,537.75 gallons.

Now that you know your pool size, are you ready to make the switch over to saltwater, so that your chlorine is operating at the lowest, safest, and most consistent levels possible? Make a smooth transition with the Salt Ways Eco Friendly Salt Chlorine Generator. It’s ultra-reliable and comes with a lifetime warranty.

Differently Shaped Pools

If you’re in this section, it’s probably because you have a pool that is pretty unique—that’s great! You might have an oval, or a classic kidney shape, or an even more artistic design. So it does require a little math, but who cares when you have a distinct pool?

The best way to calculate a uniquely-shaped pool is to break it down into other parts. That kidney shape, for instance, you might take as two circles. That sort of cubic, sort of squiggly pool could be considered two rectangles and one square. Go ahead and act like you’re calculating the volume for a few different pools, add those volumes together for the final result and then voila, you’ve got it.

Numbers Not Doing It For You? Better Make a Call

If your distinctly-shaped pool doesn’t break up well into other shapes, or if you’re just not feeling like reliving middle school right now, you can always call in a professional. I know it costs, but it’ll save you a lot of money in the long run to treat the pool you actually have, not the approximations you guess.

And who knows? There might be a teenaged math genius in your neighborhood who could use some gas money. If you’re hesitant to call in a professional, there’s no harm in asking around.

Now that you’ve calculated your pool size, is it evident your pump isn’t a good fit? Try the Copper Force Above Ground Pool Pump, which has a start capacitor and different horsepower options. According to customer Doug Paar, “The pump is very quiet and has good pressure. I would recommend.”

how to calculate your pool size

Now You’ve Got Some Feet to Stand On

Alright, so you know how many gallons your pool contains. And guess what? Unless you move or get an entirely new pool, you never have to do this math again. So you can forget the last ten minutes forever—just make sure you keep that final number handy for when you’re adding chemicals or buying equipment. And hey, wouldn’t it be nice to dive into thousands of gallons of clean water right about now? Enjoy.


For additional information on pool pump costs, you can check this article. What size pump do you need for your pool? Learn more here.

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