How many gallons is your pool?
Almost every decision about a pool starts with its volume: how long to run the pump, how much of anything to add, and what a repair is going to cost. Measure three things and this works out the rest.
The longest run, wall to wall.
At the widest point.
Same as shallow if the floor is flat.
Your pool holds about
18,000gallons
- Surface
- 512 sq ft
- Perimeter
- 96 ft
- Average depth
- 4.8 ft
How long to run the pump
Every gallon has to pass the filter to get cleaned, so run time is a function of volume and flow rather than a rule of thumb.
Most residential single-speed pumps move 50 to 80.
- Texas summer
- 9hours a day
- Winter
- 4 hours a day
- One full turnover
- 5.1 hours
What one adjustment costs at 18,000 gallons
These are single steps, so double them for a two-step move. Add chemicals one at a time with the pump running, and never put acid and chlorine in the water together.
Raise chlorine by 1 ppm
Pool shock, 73% shock
3 oz
Raise alkalinity by 10 ppm
Sodium bicarbonate, sodium bicarbonate
2.7 lb
Lower alkalinity by 10 ppm
Muriatic acid, 31.45% acid
46 fl oz (about 6 cups)
Figures are the standard trade rates for these products. Always test the water first, add less than you think, and re-test before adding more.
Measuring it properly
Three numbers, one tape measure
Length and width
The longest run wall to wall, and the widest point across. Measure at the waterline rather than across the coping, which adds a foot on every side.
Both depths
Stand a pole on the floor at the shallow end and again at the deepest point, and mark the waterline on it. Guessing the deep end is the single biggest source of error.
Shape
Rectangle and round are exact. Everything else is scaled down from the box the pool would fit inside, which is close enough for weekly chemistry.
Questions we get asked
- How do I measure a pool that isn’t a rectangle?
- Measure the longest run and the widest point, as though the pool sat inside a box. The calculator scales that box down by the share the shape actually fills. For kidney and freeform pools that’s an estimate rather than a formula, so treat the answer as accurate to within about 10%.
- Why does the average depth matter so much?
- Volume is surface area times average depth, so a foot of depth is worth as much as several feet of length. Average the shallow and deep ends. If the pool has a small deep hopper rather than a gradual slope, the real volume will be slightly under what this shows.
- Do I need the exact number?
- Close is enough for weekly chemistry, because doses are adjusted against a test result rather than calculated once and trusted. It matters most when draining, when replacing a heater, and when adding stabilizer, which is the one chemical you can’t take back out without dumping water.
- Why is my pool losing water?
- About half an inch a day is normal evaporation in a North Texas summer, with nothing wrong at all. The quarter-inch figure that circulates online comes from milder conditions than ours. Consistently more than half an inch, or a noticeable loss in winter, is worth a call before it becomes a repair, and the leak calculator will settle it in 24 hours.
Would you rather somebody else did the arithmetic?
Weekly service means the water gets tested and dosed against these numbers every visit, and you get a report showing exactly what was read and what was added. Cancel anytime.
Free tools
The rest of the arithmetic
What does a pool really cost to own here?
All five lines, not just the service rate: electricity, water, chemicals, filter cleaning, and the replacement reserve nobody puts on a quote. Prices your pool both ways, doing it yourself and having it done.
Price my poolHow long should the pump run, and what’s that costing me?
Turns your pool's volume and your pump into a run schedule and a monthly electricity figure, then shows what a variable-speed pump would save and how long it would take to pay for itself.
Work out my run timeWhat do I add, how much, and in what order?
Enter what your test kit read and get an ordered correction plan with real doses for your volume. Alkalinity before pH, sanitizer last, and never two things that shouldn’t meet.
Balance my waterIs my pool leaking, or is that just a Texas summer?
The bucket test, done properly. Two measurements 24 hours apart tell you whether the water is going somewhere it shouldn’t, and what that’s costing you a month if it is.
Run the bucket test