While it may seem like a frivolous calculation that you’ll never actually need (like most of geometry class), knowing how to calculate your pool’s surface area and volume can be invaluable when making decisions like how much pH adjuster to add, or what balance of chemicals your pool will need. Here’s how to do this seemingly difficult math problem easily.
Calculating Surface Area
Normally, you’ll only need to know how many gallons of water are in your swimming pool. But you can’t go straight to that calculation. First, you need to calculate the surface area of your pool. And while volume may seem daunting, surface area is easily calculated, especially if you have a rectangular pool. If you do, simply measure the width of your pool, then multiply by the length of the pool (make sure you stick to the same units, trying to switch between inches and centimeters has made some of the world’s smartest people make some dumb mistakes). This will give you the surface area.
Surface Area Of Non Rectangular Pools
However, many pools are not rectangular, and if yours isn’t, you’re likely still scratching your head as to just how big your pool is. If your pool follows a general geometric shape-a triangle, a pentagon, etc-then you can use the mathematical formulas for finding the surface areas of those shapes to find your pool’s surface area. But what if your pool is L-shaped, or rounded, or has some other odd shape?
If you can find a way to break up your pool into smaller rectangles or other geometric shapes, do so. This will allow you to take the surface area of each smaller piece and add it together. For example if you had an arrow-shaped swimming pool whose surface area you wanted to calculate, you’d first take the area of the rectangle behind the head of the arrow, then divide the width of the triangle by its height to get its area. These two together are the surface area of your pool.
Calculating Average Depth
Next, you’ll want to take your average depth. There’s a few schools of thought on this, but of course, the general rule applies, and the more in-depth and precise you are in your calculations, the more accurate your numbers will be.
You can simply take the deepest and shallowest depths in your pool and add them together then divide by two. This will give you a constant number that represents the ‘average’ depth of your pool. Or, you can measure the flat area in the shallow and deep ends of the pool, and then take the area of the slanted region, and find the slope. This is a much more involved approach, and should only be used if you really enjoy trigonometry or your calculations have to be perfect (if you need the pool for medical reasons, for example).
Once you’ve found your average depth, multiply this by the surface area of the pool. Your answer will come out in cubic feet or meters, but it is not the final answer! Remember that you still have to convert cubic feet or meters into gallons or litres, to properly adjust your chemicals as needed.
In general, there are about 7.5 gallons of water in 1 cubic foot. The Metric system makes things much easier, as you can simply use the conversion that 1 cubic meter of water is 1000 liters of water, so your calculations will be done at this point.
You can use the surface area and volume of your pool to make many decisions about its future. Maintaining a larger pool costs more money, for example. If you choose to renovate your pool, you might decide to enlarge it to reflect your rising quality of life, or you might decide to make it smaller to accommodate more yard space. Either way, your properly maintained pool will be a source of joy and pride for as long as you have it.
Warren Isaac is an expert on pool area and volume calculations. As a swimming pool repairer Warren always gets asked “how do I calculate my pool volume?“