Exact Pool Measurements

by Cathy Hurley
(Bayonne, nj 07002)

How many feet across is an 18 foot round pool?



Hi Cathy. That's actually a pretty good question, as simple as it sounds. When it comes down to an actual measurement all pools are slightly different.

On this page

Above Ground Swimming Pool Installation

you can see a photo where I am connecting the bottom rails and have a tape measure in one hand.

As I am connecting the bottom rails, say for an 18' pool, I am also setting each rail at the 9' mark on my tape measure. The tape is drawn from a center point that I have been using since I started clearing and leveling the ground. My initial work has all been done with a ten foot radius to allow plenty of working room around the pool.

As I am setting each rail at 9' exact I get back to the point where I started. Here I will either have to much rail or not enough. So if I am four inches over I can't just take and push the rails out at my last connection and call it good, I would then have an oval shaped pool, or at least one out of round. I have to go back and push all the rails out by maybe an inch or so. Now I have a round pool and all the connections made. I also have a pool with a radius of 9' 1".

If it goes the other way, not enough rail, I may wind up with a radius of 8' 10". So while most 18' pools have a radius of somewhere close to 9' few are exactly 9'.

The important thing is that you keep the pool perfectly round. You may set all the rails just right, and adjust all the rail gaps to where you think they are perfect, but when you install the wall it does not fit. Let's say the wall is 3" short. You could make up three inches at your last connection and have a pool that was not round or you could do it the correct way and take the wall completely down and close the gaps at each connection, and moving the track in a touch, keeping the gaps uniform and the pool round.

So, there is no exact measurement, and until you get the wall up you will not know for sure what that measurement should be, but as frustrating as it may be, always keep it round and the gaps uniform.

gaps in pool bottom rails
The importance of the pool bottom rail gaps is not realized until you are installing the top rails. Most pool bottom rails slide into a footplate and up against a stop of some sort. They are then back out to create an eighth in gap or so. The gaps vary from manufacturer to manufacturer and from pool to pool and it's pretty much a guessing game.

It is important in the end that all the gaps are the same. They determine the distance between each upright. The top rails all have pre drilled holes in them so their distance is set. If the distance between your uprights is not all the same the top rails are not going to fit the way they should. This causes major problems during the final phase of your pool construction.

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