How to calculate the flow rate in a swimming pool?

Flow Rate (in gallons per minute) = Pool Volume (in gallons) ÷ Turnover Time (in minutes)

The turnover time is the amount of time it takes for the pool’s entire volume of water to pass through the filter and be recirculated back into the pool. The recommended turnover time for a pool varies based on factors such as pool size, bather load, and climate, but it typically ranges from 6 to 8 hours.

To calculate the pool volume, use the appropriate formula based on the shape of the pool (as discussed in the previous answer). Once you have calculated the pool volume, you can determine the required flow rate by dividing the pool volume by the turnover time (converted to minutes).

For example, let’s say you have a rectangular pool that is 20 feet long, 10 feet wide, and 5 feet deep. Using the formula for rectangular pools (Volume = Length x Width x Depth), the pool volume would be:

Volume = 20 x 10 x 5 = 1,000 cubic feet

To convert cubic feet to gallons, multiply by 7.48 (since 1 cubic foot equals 7.48 gallons):

Volume = 1,000 x 7.48 = 7,480 gallons

If you want a turnover time of 8 hours (or 480 minutes), the required flow rate would be:

Flow Rate = 7,480 ÷ 480 = 15.58 gallons per minute

Therefore, to achieve a turnover time of 8 hours for this rectangular pool, a flow rate of at least 15.58 gallons per minute is required. This flow rate can be used to select an appropriately sized pump for the pool.