Total Dynamic Head (TDH) Calculator
Work out the head a pump has to deliver at your flow rate. Enter the flow, the pipe, the vertical lift, the pressure you need at the outlet and the fittings on the line, and the calculator adds up static lift, pressure head, pipe friction, fitting losses and velocity head into the total dynamic head in feet, metres and psi.
From the water level at the source (pumping level in a well) up to the highest discharge point. Negative if the source is higher.
Fittings on the Line
Enter values to calculate
Total dynamic headFree download
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Schedule 40 pipe sizes, water flow in GPM and LPM at four design velocities, and recommended velocities by application. One PDF, made to pin above the bench.
How It Works
Total dynamic head is the energy a pump has to add to each pound of water, expressed as a height of water column, the unit pump curves use. It is the sum of the fixed static part, which is there even with no flow, and the dynamic part, which grows with flow.
TDH Formula
TDH = Hstatic + Hpressure + Hpipe + Hfittings + V²/2g
- • Static lift: vertical distance from the source water level to the discharge point
- • Pressure head: pressure needed at the outlet, converted with 1 psi = 2.31 ft of water
- • Pipe friction: Darcy–Weisbach with the Colebrook friction factor, the same method as our pressure drop calculator
- • Fittings: K = n × fT for each fitting (Crane TP-410), times the velocity head
- • Velocity head: V²/2g, the energy the water leaves the pipe with
Worked Example
20 GPM through 200 ft of 1-1/4" Schedule 40 PVC (1.363 in average bore), lifting 100 ft, with 40 psi needed at the outlet, four 90° elbows, one swing check valve and one gate valve:
- • Static lift = 100.00 ft
- • Pressure head = 40 × 2.3105 = 92.42 ft
- • Pipe friction: velocity 4.40 ft/s, f = 0.0214, so 11.31 ft
- • Fittings: K = (4 × 30 + 100 + 8) × fT = 4.78, so 1.43 ft
- • Velocity head = 0.30 ft
- • TDH ≈ 205.5 ft (62.6 m, 88.9 psi)
Water power = 20 GPM × 205.5 ft ÷ 3960 = 1.04 hp. Divide by the pump efficiency for the shaft power, or use the pump power calculator.
Pressure Head in the TDH Sum
For water at 20°C, 1 ft of head = 0.433 psi and 1 psi = 2.31 ft. The same figures convert a pressure gauge reading into the head a pump curve shows. For other liquids or units, use the psi to feet of head converter or the feet of head to psi converter.
| Head (ft) | psi | Head (m) | bar |
|---|---|---|---|
| 10 | 4.3 | 3.0 | 0.30 |
| 20 | 8.7 | 6.1 | 0.60 |
| 50 | 21.6 | 15.2 | 1.49 |
| 100 | 43.3 | 30.5 | 2.98 |
| 150 | 64.9 | 45.7 | 4.48 |
| 200 | 86.6 | 61.0 | 5.97 |
| 300 | 129.8 | 91.4 | 8.95 |
Fitting Loss Coefficients (Crane TP-410)
Each fitting loses K velocity heads, with K = n × fT. n is the fitting's equivalent length in pipe diameters and fT the fully turbulent friction factor of clean steel pipe of that size, so K falls as the pipe gets bigger.
| Fitting | n | K at 1" | K at 2" | K at 4" |
|---|---|---|---|---|
| 90° elbows | 30 | 0.67 | 0.57 | 0.49 |
| 45° elbows | 16 | 0.36 | 0.30 | 0.26 |
| Tees, flow through run | 20 | 0.45 | 0.38 | 0.32 |
| Tees, flow through branch | 60 | 1.34 | 1.14 | 0.97 |
| Gate valves | 8 | 0.18 | 0.15 | 0.13 |
| Ball valves (full bore) | 3 | 0.07 | 0.06 | 0.05 |
| Swing check valves | 100 | 2.24 | 1.89 | 1.62 |
| Globe valves | 340 | 7.62 | 6.43 | 5.52 |
fT = 0.0224 (1"), 0.0189 (2") and 0.0162 (4") Schedule 40, computed from clean steel roughness. The calculator uses the fT of the pipe you pick, for every material, which is slightly conservative for smooth plastic fittings.
FAQ
Answers to common questions about pump head.
Frequently Asked Questions
What is total dynamic head?
Total dynamic head (TDH) is the total head a pump must add at a given flow: the static lift from the source water level to the discharge point, plus the pressure needed at the outlet, plus friction in the pipe and fittings, plus the velocity head. It is expressed in feet or metres of water, the unit pump curves use.
How do I turn the outlet pressure into head for TDH?
For water, psi = feet × 0.433 and feet = psi × 2.31. So 100 ft of head is 43.3 psi, and 40 psi is 92.4 ft of head. In metric, 10.21 m of head is 1 bar.
What is the difference between static head and dynamic head?
Static head is set by elevation and pressure and is there even at zero flow. Dynamic head, the pipe and fitting friction plus velocity head, grows roughly with the square of the flow. That is why TDH is always quoted at a particular flow rate, and why a pump runs where its curve crosses the system curve.
Where do I measure the lift from for a well pump?
From the pumping water level, the lowest level the water falls to while the pump runs, up to the highest point the water is delivered to. Measuring from the static water level understates the lift. Where the pump sits does not change it: a submersible pump below the water still lifts from the pumping level, and a surface or jet pump above the well has to pull the water up to itself as part of the same lift.
How do I choose a pump from the TDH?
Pick a pump whose curve delivers your flow at or above the calculated TDH, ideally close to its best efficiency point. Water horsepower = GPM × TDH in feet ÷ 3960; divide by the pump efficiency to get the shaft power the motor must supply.
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