Spa and Swimming Pool Size Formulas and Calculations

From time to time, a person may need to know a spa or pool size formula to calculate gallonage for pump run time or surface area for heating or painting for example. I will constantly add to this page as more people ask for specific calculations.

Gallonage

2)Round: diameter x diameter x average depth x 5.9 (liters = meters x 785)

3)Oval: length x width x average depth x 6.7 (liters = meters x 893)

4)Kidney: (Widest point of pool + narrowest point of pool) x average depth x 3.37 = gallonage

Interior Surface of Pool in Square Feet

Believe it or not, this simple formula will work on almost any shape of shell!

Surface Area of Pool Water in Square Feet

2)Round: radius(1/2 diameter) x radius x 3.14

3)Oval or Roman: 1/2 length x 1/2 width x 3.14

4)Kidney shape: length x width x 0.75

Amount of D.E. to Add to Filter

Filter square footage divided by 5 equals number of scoops or 1 pound coffee cans of D.E. to add to skimmer.

Energy/Cost to Run Pump

Amps x volts divided by 1000 = kilowatts

Kilowatts x hours per day pump is run x kilowatt hour energy cost = cost per day to run pump.

Note: you may have two amp values listed on your motor; the higher value is for 115 volts, the lower value 230 volts. (Because 230 divides the amps between two wires,which puts less stress on the wiring also)

The link below will take you to pump energy cost calculator, and also let you compare an average energy efficient pump to a variable speed pump:

Calculating the energy cost to run your pump

Pump Affinity Law

Speed RPM (revolutions per minute) = Flow GPM (gallons per minute)

Speed RPM = Power3

Example: Reduce speed

3000 RPM -> 1500 RPM

1/2 Speed RPM = 1/2 GPM

1/2 Speed RPM = 1/2 x 1/2 x 1/2 = 1/8 energy used

3000 RPM -> 1000 RPM

1/3 Speed RPM = 1/3 GPM

1/3 Speed RPM = 1/3 x 1/3 x 1/3 = 1/27 energy used

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