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.
- One full turnover
- 5.1 hours
- Texas summer
- 9 hours a day
- Winter
- 4 hours a day
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
Liquid chlorine, 12.5% liquid
22 fl oz (about 3 cups)
Raise alkalinity by 10 ppm
Baking soda, sodium bicarbonate
2.7 lb
Lower alkalinity by 10 ppm
Muriatic acid, 31.45% acid
23 fl oz (about 3 cups)
Raise calcium by 10 ppm
Calcium chloride, 77% flake
2.3 lb
Raise stabilizer by 10 ppm
Stabilizer, granular
1.5 lb
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 is not 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 is 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 cannot take back out without dumping water.
- Why is my pool losing water?
- Between one quarter and one half an inch a day is normal evaporation in a North Texas summer. Consistently more than that, or any loss at all in winter, is worth a call before it becomes a repair.
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. No contracts.