Pool Pump Size Calculator: What’s the Best Pump Size for Your Pool?

Are you having a hard time selecting the best size pool pump for your above or inground pool? It doesn’t have to be complicated anymore.

Your best pool pump size must meet your minimum and maximum flow rates, which you get by finding the pool volume first. And for you to get all these, you have to do a series of calculations. In the end, you will have the ideal min-max flow rate range to help you find the perfect pool pump size for your swimming pool.

Below are few calculations that will break down the search and give you enough certainty that you’re buying the right size pump.

Calculations to Help You Figure Out the Best Pool Size Pump

Calculate Your Pool Volume

First up, you need to figure out how many gallons of water are in your swimming pool. This calculation differs based on pool shape but is pretty straightforward. Use our pool volume calculator below, and then we’ll start calculating the minimum flow rate you need for your pump.

The first metric is the pool volume which will help you determine the minimum and maximum flow rates required.

Pool capacity and calculations differ with the pool’s size and shape. There is a rectangular, circular, oval, and irregular-shaped pool. Which one is yours?

If you want a straight forward method, use the pool volume calculator below:

If you want to do the calculations yourself, here are the formulas to help you determine how many gallons of water your pool holds.

Constants and terms used:

7.5 = Number of Gallons Present in a Cubic Foot
r = distance across the center of a circular pool divided by 2
π = a constant used in calculating area or volume of a circle (3.14 or 22/7)

Square or Rectangular Shaped Pools w/Uniform Depth

(Length) x (width) x (depth) x 7.5 = volume (in gallons)

Square and Rectangular Pools w/Shallow and Deep Ends

Length x width x AVERAGE DEPTH x 7.5 = volume (in gallons)
AVERAGE DEPTH = (depth of deep end + depth of shallow end)/2

Circular Pools w/uniform depth

π (3.14) x radius squared(r2) x AVERAGE DEPTH x 7.5 = volume (in gallons)

Circular Pool w/Deep and Shallow Ends (Even though they are rare, they exists)

π (3.14) x radius squared(r2) x AVERAGE DEPTH x 7.5 = volume (in gallons)
[Simplified: π x r2 x average depth x 7.5 = volume (in gallons)]
AVERAGE DEPTH = (depth of deep end + depth of shallow end)/2

Kidney or Irregular Pools

Divide your swimming pool into smaller regular shapes, then use the above formulas to calculate their volumes. Once you have the volumes of the smaller pieces, add them up.

Calculate the Minimum Flow Rate

Now that you have your pool volume, it’s time to move to the next step; calculate the minimum flow rate to expect from your pool pump in Gallons per Minute (GPM). You could also use the Gallon per Hour (GPH).

The minimum flow rate gives you the number of gallons pumped per minute or per hour to meet the pool turnover.

The pool ‘turnover’ rate gives you the minimum time it takes for the whole pool water to be pushed by the pump through the filter and back to the swimming pool.

Here you will need to use the pool capacity and the number of your pool’s turnover cycles per day. Experts in the industry recommend you give your chlorine or saltwater swimming pool two turnovers per day.

When determining the best turnover for your swimming pool, you have two options:

• Run the pool pump for 24 hours per day, which decreases the flow rate needs.
• Run the pump twice a day with a turnover rate of 6-, 8- or 10-hour cycles.

What you need to do here is to consider balancing electricity consumption with the pump horsepower. If you use a low horsepower pump for long, you gain better water chemistry balancing. However, your electricity bills will be over the roof.

With higher horsepower, the run time reduces as doing so, the power consumption decreases. However, the pool chemistry balancing doesn’t do well.

That’s why you might want to consider getting yourself a variable speed pump. It changes its speed up and down depending on the need at hand. It’s much better for pool chemistry balancing, improved turnover, and saves on energy bills.

Calculating the minimum flow rate is quite simple; all you need is your pool’s volume in gallons and divide it by the turnover in minutes (GPM) or hours (GPH). If you don’t want to go along with all the math, below is a simplified minimum flow rate calculator.

If you’re a hands-on kind of a guy, here is the formula for calculating the minimum required flow rate:

Pool Volume (Gallons) / Turnover rate (Minutes) = Min Flow Rate (GPM)
Pool Volume (Gallons) / Turnover rate (Hours) = Min Flow Rate (GPH)

Calculate the Maximum Flow Rate

The maximum flow rate is the highest water flow your pool plumbing system, and other equipment can support. If you bought a pump with a higher GPM than your pool, you risk bursting the system and wasting your electricity.

If you bought an above-ground pool, the maximum flow rates would be in the documentation. The same applies to pool equipment.

But if you built the swimming pool from scratch or if these details aren’t available, here is how to estimate your system’s maximum flow rate:

a) Plumbing

The best place to start is at the pool plumbing and work your way to the pool filter and other equipment you may have along with the pool filtration and circulation.

You want to make sure the pool pump you use doesn’t blow out your system. And the maximum flow rate of the pool plumbing will depend on the pipe size used. That’s why it’s a must that the system be labeled clearly.

If the contractor forgot to label, make a call. You can also the following standard values used in pool plumbing.

But remember, the plumbing system in your swimming pool might be different in size. Some pipes might be smaller or bigger than your samples. So, while estimating its maximum flow rate, take the smallest value you get. It will help you avoid the risk of damaging the system.

b) Pool Filter

The next stop is the pool filter. And as you might already know, pool filters are of three types. There is a sand filter, cartridge, and DE filter, and they all have different maximum flow rates.

It’d be best to stay under the filter’s maximum flow rate as going overboard can damage it. Below is a breakdown of the various pool filter flow rates:

Sand Filters: Typically, sand filters come with maximum flow rates that range from 19GPM – 20GPM per square foot of their surface area.

Cartridge Filters: With cartridge filters being more significant in size and less precise, their maximum flow rates averages between 0.3 to 0.4 GPM per square foot of their surface area. The table below shows these estimates.

Diatomaceous Earth (DE) Filters: this is the third and final type of pool filter. It’s approximately 1.75 maximum flow rate per square foot of its surface area. The estimates of the systems available are shown in the table below.

Determine Required Minimum and Maximum Flow Rates

So far, you already have the pool’s maximum and minimum flow rates, but you need to know the ideal range and use it to select the correct size pool pump.

Assuming you have a 50,000-gallon inground pool and two 12-hour turnovers in a day, the minimum flow rate 69.44 GPM.

Assuming the same swimming pool uses a 300 ft2 cartridge filter of 81 GPM maximum flow rate and a 2.0-inch plumbing system of 73 GPM maximum flow rate, take the lower value of these ranges. It will help avoid overworking your pool circulation and filtration components.

The maximum flow rate for such a pool would be 43 GPM (for the 1.5” pipe), the smallest in all the categories. That would mean your max-min flow rate range is 69.44 – 73 GPM.

Estimate Total Resistance

The total resistance to water flow, measured in ‘feet of the head,’ tells you how the other pool equipment such as the vacuum, heater, and the other can affect the pump flow rate.

If you higher the total resistance to flow, you need a powerful pool pump to overcome it. Most above-ground pools have 30 Feet of Head, and inground pools have 50 Feet of Head.

Best Pump Size for Your Pool

And there you have it, everything you need to know the exact pool pump size to buy. These calculations will ensure you buy the perfect size and also make sure you match the necessary metrics for excellent pool pump performance. If you’re not into math calculations, enter the required details in the calculator’s fields and hit the calculate button. It’s that easy!