Irrigation Pump Sizing Calculator: Choosing the Right Pump

Flow rate is the volume of water moving through the system, in gallons or litres per minute. Calculate it by adding the demand of every zone running simultaneously. This figure defines your baseline pump requirement — and drives Dosatron model selection.

Operating pressure is the force needed to push water through pipes, filters, valves and emitters. Each outlet type has its own range: sprinklers, micro-sprays and drip emitters all operate differently.

Dosatron dosing pumps have their own minimum and maximum pressure limits. Staying inside that window is what keeps dosing stable.

TDH is the total resistance the pump must overcome — elevation change, pipe friction loss, filters and fittings, and required outlet pressure. Pipe diameter and total run length both influence friction loss and should be factored in.

TDH = Elevation Head + Friction Loss + Required Operating Pressure

Elevation head is the vertical distance between the water source and the highest outlet. Where pipe runs, fittings and elevation vary across the system, a friction loss calculator gives a more accurate TDH estimate. Accurate TDH prevents both pressure loss at the emitter and unnecessary strain on the pump.

Step 1 — Flow rate. Four zones, 5 GPM each, all running at once:

5 GPM×4 zones=20 GPM 

Step 2 — Pressure requirement.

The pump needs to deliver roughly 20 GPM at 60 PSI. That's the operating point a sizing calculator uses to shortlist suitable pumps.

Step 3 — Convert PSI to feet of head.
Some pump curves are plotted in feet rather than PSI:

1 PSI = 2.31 feet of head
60 PSI × 2.31=138.6 feet 

So the pump should deliver 20 GPM at approximately 140 feet of total dynamic head.