How To Size A Pool Pump
Calculating the size of your pool is incredibly important. If you get a pump that is too small, it will not completely do the job and you will have a dirty, unswimmable pool. If you get a pump that is far too large, you will be paying way to much for the pump system itself, as well as more money than needed to operate the larger pump. A properly sized pool pump with save you a ton of money give you the reliable performance that you demand.
Step 1: Determine The Number Of Gallons In Your Pool
The calculation for determining the number of gallons of water in your pool varies by the shape of the pool. The four most common shapes and their calculations are shown below (use the one closest to the shape of your pool:
Rectangular
- Avg Depth = (Deep End + Shallow End) / 2
ex: Avg Depth = (10ft + 3ft) / 2 = 6.5ft - Gallons = Length x Width x Avg Depth x 7.5
ex: 30ft x 15ft x 6.5ft x 7.5 = 21,937 gallons
Round
- Avg Depth = (Deep End + Shallow End) / 2
ex: Avg Depth = (10ft + 3ft) / 2 = 6.5ft - Gallons = Diameter x Diameter x Avg Depth x 5.9
ex: 20ft x 20ft x 6.5ft x 5.9 = 15,340 gallons
Oval
- Avg Depth = (Deep End + Shallow End) / 2
ex: Avg Depth = (10ft + 3ft) / 2 = 6.5ft - Gallons = Long Diameter x Short Diameter x Avg Depth x 5.9
ex: 30ft x 15ft x 6.5ft x 5.9 = 17,275 gallons
Kidney
- Avg Depth = (Deep End + Shallow End) / 2
ex: Avg Depth = (10ft + 3ft) / 2 = 6.5ft - Gallons = (Long Width + Short Width) x Length x Avg Depth x 3.38
ex: (15 + 10) x 30 x 6.5ft x 3.38 = 16,477 gallons
Step 2: Determine How Many Gallons Per Hour Needed
You should determine the gallons per hour (GPH) needed to clean all of the water in your pool in 8 hours (typical day length).
- GPH = Gallons / 8 hours
ex: 21,937 gallons / 8 hours = 2,742.2 GPH
Step 3: Convert GPH to GPM
Most pool pumps are specified in gallons per minute (GPM), so we will need to convert our gallons per hour to gallons per minute.
- GPM = GPH / 60 minutes
ex: 2,742.2 GPH / 60 minutes = 45.7 GPM
Step 4: Determine The Avg Feet Of Head
Now we must calculate the avg distance from your suction lines (skimmers, main drain) back to your pool pump. You will need a pump that can move water this distance without a problem for the system to work properly.
Below is an example of a pool with 3 suction lines (2 skimmers and a main drain): we will calculate the distance of each line as well as the avg length.
- Skimmer 1: 5ft + 15ft + 25ft + 15ft + 10ft = 70ft
- Skimmer 2: 15ft + 10ft = 25ft
- Main Drain: 25ft + 20ft = 45ft
- Average Head: (70ft + 25ft + 45ft) / 3 = 46.6ft
Step 5: Additional Considerations
Depending on your specific pool, you may need to incorporate any of these other considerations in order to get the proper sized pool pump.
- If your pump includes fountains, spas, waterfalls, solar heating, and infloor cleaning systems, you may require additional GPM and therefore a large horsepower pump than your standard calculations have indicated (our team can assist in making these determinations).
- If you require more than 60 GPM you will need 2″ piping instead of standard 1-1/2″ piping as 1-1/2″ piping has a physical limit of 60 GPM.
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