Almost every pool task — balancing chemicals, shocking, adding salt, sizing a heater or pump — is dosed "per X gallons." Guess the volume and you either waste product or throw your water chemistry off. Here's how to nail it.
The basic formula
For a rectangular pool: length × width × average depth × 7.48, with the dimensions in feet. The 7.48 converts cubic feet to gallons. Our pool volume calculator does it instantly.
What "average depth" means
If your pool has a shallow and a deep end, average depth is simply the two added together and divided by two. A pool that's 3 ft at the shallow end and 7 ft at the deep end has an average depth of 5 ft.
Oval and round pools
- Oval: calculate it as a rectangle, then multiply by about 0.89.
- Round: use π × radius² × average depth × 7.48 (radius is half the diameter).
Why the number matters
Pool chemicals are labeled by volume — for example, "add this much per 10,000 gallons." If you think your 19,000-gallon pool is 15,000, you'll under-dose chlorine and over-dose something else, fighting cloudy water all season. Measure once, write the number on the equipment pad, and dosing becomes simple math.
Measure the water, not the walls
Use the inside water dimensions, not the outside of the coping or walls. A few inches off on each side adds up across a big pool. Once you have your gallons, keep it handy — you'll use it every time you open a chemical bottle.