Ask the General- How Much Water Fits in my Inground Fiberglass Pool?

Ask the General- How much water fits in my inground fiberglass pool

Dear General-

Our pool is fairly new. One of our neighbors recently asked me how much water fits in my inground fiberglass pool and my answer was, “Um… a lot.” I realize that’s probably not the level of detail I should know about my own pool. But math is really not my strong suit. Can you help?


Wondering about Water in Wabash


Dear Wondering-

Most of us don’t spend a ton of time doing math to calculate the water volume in our pools. (It’s hard to work a calculator under water.) The easy answer is that your pool installer most likely gave you this information when installing the pool. However, you might have lost that information in your excitement to start swimming. So let’s wade into this water question…

Why Do You Need to Know Your Pool’s Water Volume?

Other than satisfying your neighbor’s curiosity, why would you need to know how much water your pool holds? Well, there are a couple of good reasons.

  1. Determining chemical usage. I know you don’t love math, but you certainly can’t begin to calculate how much volume of any chemical you need to bring your water into balance if you don’t know how much water you’re putting it in. So, if you’re having trouble getting your water chemistry balanced, you could be basing it on incorrect volume.
  2. Refilling your pool. If you’ve had to have your pool drained for any reason, you’ll need to know how much water it’s going to take to fill it back up.
  3. Choosing accessories and equipment. If, for example, you’re considering getting a heater for your pool and you’re shopping online, guess what question you’re going to have to answer? You guessed it–how much water are you looking to heat? The same is true for pool pumps and filters–you’ll need to know the volume of water in your pool to choose the proper capacity for equipment.

How much water fits in my inground fiberglass pool How Can You Determine Your Pool’s Water Volume?

As I mentioned earlier, you probably have this information in your records from your pool installation. But if you’re like me, you have no idea where that paperwork is. So, here are a couple other ways to find out.

  1. Ask a pool professional. All testing centers have the ability to determine pool volume with a chart, computer, or simple calculation. A pool and spa service technician should know how to make these calculations easily and routinely, either by taking a look at the pool itself or reviewing your pool’s specifications. They will consider surface area, volume, deck size and allowable bather load.
  2. Ask your pool’s manufacturer. Check out the customer support on your pool manufacturer’s website. If you can’t find the information for your pool on their website, give them a call. They should be happy to provide you with this information.
  3. Do the math. If you can’t get the information from a pool professional or your manufacturer (or if you really just want to know how this all works) here’s a bit of reference:
  • 1 cubic ft of water contains: 7.48 gallons
  • 1 cubic ft of water weighs 62.4 lbs
  • 1 gallon of water equals .134 cubic ft.
  • 1 gallon of water weighs 8.33 lbs
  • 1 (PPM) part per million represents 8.3 pounds of chemical per million gallons.

Sample calculation:

A train is leaving the station traveling 60 mph. (Ha… I’m just kiddin’…) Seriously– here’s how we do it:

The simplest calculation for pool volume is width x length x average depth. (You’ll get the rough average depth by adding the depth of the deep-end and the shallow-end together and dividing by 2.) That number will give you the cubic feet. Take that number times 7.5 gallons, and that will give you the total water volume of your pool.

So, for example, take a rectangular pool that’s 16’ x 32’ x 6’ deep with a 3’ deep shallow-end. If you apply this formula to this particular pool, you’ll find it holds approximately 18,000 gallons of water. That might not be exact, but it’s a lot more specific than “a lot.” Plus, it will really impress your neighbor.

Fall is approaching, and pool season is starting to slow down here in the Midwest. The kids are back in school, the nights are getting cooler, and the days are getting shorter. But there’s still time to enjoy the pool. I’ve got my heater set to the perfect setting for my pool’s water volume, so I’m going to grab a float, turn on the heater and hop in.

Until next time-

The General


Who is The General?

The man, the myth, the legend….we just call him The General. His organized, systematic approach to pool installations over the years had his crew members calling him “The General” and it stuck. The General has over 30 years’ experience in the pool and spa industry, working for one of Pool and Spa News’Top 50 Pool Builders.”

Over that time, he designed, sold, project-managed and installed over a thousand inground swimming pools. As a pool owner himself, he’s the perfect authority to give you the inside scoop, with amazing tips and tricks to make pool ownership a breeze!