Calculating pump size


New member
Mar 7, 2020
Bountiful, UT
Building a new pool. About 15,000 gallons. I think I should be using 2" PVC. My pool pump will be about 70' from the point that the water comes out of the pool. Lastly, the pump will be about 10' higher than the point that the water comes out of the pool.
In case you couldn't tell, I'm a newbie at this and honestly don't know squat.
How is pump size calculated from this info? Is there more info needed? If so, what is it?
Thanks for the help and I look forward to being a member of this group!


Gold Supporter
TFP Guide
Jul 21, 2013
Northern NJ
Welcome to TFP.

Any water features? Spa? Heater? Solar?

You really need a complete design of the pool and equipment to specify the minimum pump HP required.

Chances are a pump around 3 HP variable speed will be able to satisfy the needs.

@mas985 thoughts?


Mod Squad
TFP Expert
Platinum Supporter
LifeTime Supporter
In The Industry
Apr 1, 2007
Sebring, Florida
Welcome to the forum:wave:
It's the height of the top of the water in the pool that the pump still 10' higher? That will be a problem but can be fixed, if so.

Use 2" pipe on the suction side for a 70' run......regardless of pump size. 1.5" is normally adequate to return water back to the pool.


TFP Expert
Mar 2, 2011
Ideally, you want the pump as low as possible.

Is the location definite or are there other possible locations?

10 feet is about a maximum the pump should ever be above the pool surface and it is best to avoid going that high.

Can you describe the pool in detail?


TFP Expert
Mar 2, 2011
Note that pump size or horsepower is not determined by distance from the pool or elevation.

Distance is irrelevant as long as the pipe is sized correctly. The pump can be a mile away as long as you use the correct size pipe.

Elevation is not really a factor because whatever you lose going one way is gained going the other way.

You should avoid having the pump significantly higher than the pool (10 feet maximum).

Elevated pumps should use larger diameter pipe on the suction (usually one size bigger depending on the details).

Elevated systems have some unique characteristics that require special treatment such as check valves and vacuum breakers. Heaters will require the addition of a flow switch to replace the pressure switch.

Below is fine and only adds pressure but no net head loss. The extra pressure can shorten the life of the pump somewhat. Heaters require the addition of a flow switch.

Pump choice is determined by the flow rate required and the total head loss.

For pipe sizing, you need to know the flow rate intended for each pipe. For suction, you want to keep the water velocity below 6 ft/sec. For returns, you want to keep the water velocity below 8 ft/sec.

Size.......6 ft/sec......8 ft/sec.
1.5"...........38...............51 gpm
2"..............63...............84 gpm
2.5............90.............119 gpm
3.0".........138.............184 gpm

As long as you keep the water velocity below 6 ft/sec on the suction and below 8 ft/sec on the pressure side of the pump, you're good for typical distances (up to 100 feet).

Going extra far requires larger pipe depending on the distance.
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