Total Dynamic Head & Size the Pump to the Real Head
Adds static lift
A pump is chosen by its head and flow — add the static lift, friction loss, operating pressure and delivery head to get the Total Dynamic Head in metres, the head your pump must deliver to water the field.
Enter your pumping system
Next: read your pump curve at the design flow rate and pick a pump whose head at that flow meets or slightly exceeds 44 m; if friction dominates the stack, upsize the pipe before buying a bigger pump.
TDH = static lift + friction loss + operating pressure + delivery head.
Total Dynamic Head — key facts
- Formula
- TDH = lift + friction + pressure + delivery
- Sprinkler pressure
- ≈ 25 m (2.5 bar) at nozzle
- Drip pressure
- ≈ 10 m (1 bar)
- Flood/furrow pressure
- ≈ 0 m
- Used with
- design flow → pump duty point
- Friction from
- Hazen-Williams + fittings
- Falling source
- size at lowest water level
- Privacy
- Runs in your browser; nothing uploaded
The one head figure that selects your pump
A pump is chosen at a flow and a head, and the head it must beat is the Total Dynamic Head — the sum of every resistance between the source and the emitter. Lift the water against gravity, push it through pipe friction, and supply the pressure the drippers or sprinklers need at the end, and add any extra height at the delivery: those four together are the TDH. Get this number right and the pump lands on its best-efficiency point; get it wrong and the field is starved or the energy is wasted.
This tool adds the static lift, friction loss, operating pressure and delivery head into a single Total Dynamic Head in metres, ready to pair with your design flow to pick a pump from its curve. Use it alongside the Hazen-Williams Friction Loss, NPSH Available and Irrigation Pump Power tools for a full pump selection.
Select the right pump
Pair TDH with flow to find the duty point.
Avoid under-watering
Size for real head so the far field still gets water.
Account for pressure
Add the head drip or sprinkler emitters truly need.
Plan for falling water
Re-run at the lowest level so flow holds in the dry.
Frequently Asked Questions
What is Total Dynamic Head?+
Total Dynamic Head is the total head, in metres of water, that a pump must produce to move your design flow from the source to the point of use. The tool adds four parts: TDH = static lift + friction loss + operating pressure + delivery head. Together they are the head the pump works against, and with the flow they fix the duty point you use to select a pump from a manufacturer's curve.
What is the difference between static lift and delivery head?+
Static lift is the vertical distance from the water surface up to the pump or the field datum — the height the water has to be raised against gravity. Delivery head is any additional elevation the water must reach at the far end, such as a tank on a stand or a field on higher ground. The tool keeps them as separate inputs so you can account for both the source depth and the destination height clearly.
Why include operating pressure in the head?+
Drip and sprinkler emitters only work at their rated pressure — a sprinkler might need 25 m of head (about 2.5 bar) at the nozzle, and a dripper around 10 m. That pressure has to be present on top of all the lift and friction, so it is added into the TDH. Flood and furrow irrigation need almost no operating pressure, so for those systems this term is near zero.
How is the friction loss found?+
Friction loss is the head the water loses dragging along the suction and delivery pipes and through fittings, and it grows with flow and shrinks with pipe diameter. You can compute it with the Hazen-Williams equation for the pipe run and add an allowance for fittings, then enter the total here. Because friction rises steeply with flow, an undersized pipe can make the friction term dominate the whole TDH.
How do I use the TDH once I have it?+
Take the TDH together with the design flow rate and read across a pump's performance curve to find a pump whose curve passes through, or just above, that flow-and-head point at good efficiency. Then check the motor power needed at that duty and confirm the NPSH available exceeds the pump's NPSH required. The TDH is the head axis of that selection — get it wrong and the pump is over- or under-sized.
What happens if I underestimate TDH?+
If the real head is higher than you sized for, the pump rides back up its curve and delivers less flow than you need — sprinklers throw short, drip lines starve at the far end, and the field is under-watered. Over-estimating wastes money on an oversized pump and motor and can push too much pressure into the system. Adding the four terms carefully, with a realistic friction figure, avoids both errors.
Is TDH the same as the pump's rated head?+
TDH is the head your system demands; the pump's rated head is what a given pump can supply. The goal is to choose a pump whose head at your flow matches the system's TDH at that flow — the intersection of the system curve and the pump curve, called the duty point. So they should be equal at the operating flow, but they are different concepts: one describes the field, the other the machine.
Does TDH change as the water level drops?+
Yes — on a well or pond where the water level falls during pumping or across a dry season, the static lift grows, so the TDH rises and the pump delivers less. For a falling source, size the pump for the head at the lowest expected water level, not the full level, or the flow will fade just when demand is highest. Re-run the calculation at the drawn-down level to be safe.