Calculate total dynamic head (TDH) for an irrigation pump by summing pumping lift, friction loss, and operating pressure. Essential for pump selection.
Total dynamic head (TDH) is the total resistance a pump must overcome to deliver water from its source to the point of use. It consists of three components: pumping lift (the vertical distance water must be raised), friction loss (energy lost to pipe and fitting resistance), and operating pressure (the pressure required at the system outlet).
TDH is expressed in feet of head and directly determines the pump's power requirement and energy cost. Accurate TDH calculation is essential for selecting the right pump curves, sizing the motor, and estimating energy consumption.
This calculator sums the three TDH components and converts operating pressure from PSI to feet of head, giving you the number you need for pump selection and energy cost estimation. Whether you are a beginner or experienced professional, this free online tool provides instant, reliable results without manual computation. By automating the calculation, you save time and reduce the risk of costly errors in your planning and decision-making process.
Incorrect TDH estimates lead to pump and motor mis-sizing. Too low means the system cannot deliver design flow. Too high means capital wasted on an oversized pump that operates inefficiently. Get TDH right the first time. Having a precise figure at your fingertips empowers better planning and more confident decisions.
TDH (ft) = Pumping Lift (ft) + Friction Loss (ft) + Operating Pressure (ft) Pressure (ft) = PSI × 2.31 Where: Pumping Lift = Drawdown level to discharge point Friction Loss = Pipe + fitting losses (from tables or Hazen-Williams) Operating Pressure = System pressure at discharge (converted from PSI)
Result: TDH = 272.4 ft
Operating pressure in feet = 40 PSI × 2.31 = 92.4 ft. TDH = 150 + 30 + 92.4 = 272.4 ft. This is the head the pump must develop at the design flow rate.
Pumping lift includes static water level, drawdown, and any elevation gain from pump to field. Friction loss increases with flow rate and pipe length but decreases with larger pipe diameter. Operating pressure depends on the irrigation system type: drip needs 8–20 PSI, sprinklers 30–60 PSI, and high-pressure guns 60–100 PSI.
Upsizing pipe by one diameter class (e.g., 6" to 8") can cut friction loss by 50–70%. The extra pipe cost is often recovered within a few seasons through lower energy use. Always evaluate pipe sizing against TDH and energy cost.
Plot your required operating point (GPM, TDH) on the pump manufacturer's curve. The ideal pump operates within ±10% of its best efficiency point (BEP). Off-BEP operation increases vibration, wear, and energy waste.
Pumping lift is the vertical distance from the pumping water level in the well to the discharge point. It includes static water level plus drawdown during pumping.
Use Hazen-Williams tables with your pipe diameter, material (PVC C=150, steel C=130), flow rate, and total pipe length. Online calculators or NRCS tables simplify this.
Pump curves are plotted in feet of head. The conversion (1 PSI = 2.31 ft) puts all components in the same unit so they can be added directly.
For surface pumps, suction lift (distance from water surface to pump inlet) is part of pumping lift. Submersible pumps in wells do not have suction lift issues.
Slightly. Warmer water is less dense and has slightly less friction, but for irrigation temperatures (40–80°F), the effect is negligible.
Select a pump with more stages (multi-stage turbine) or boost pressure with a secondary pump. Reducing friction loss by upsizing pipe is often the most cost-effective solution.