What is total dynamic head?

Total dynamic head (TDH) is the total resistance a pump must overcome: the static lift, the friction loss through pipe and fittings, and the velocity head. It is the value you match against a pump's performance curve at your design flow.

How is friction loss calculated?

This tool uses the Hazen-Williams equation, the standard for water at normal temperatures. Loss grows with flow raised to the 1.852 power and falls steeply with diameter, so small pipes and high flows dominate the friction term.

What is equivalent length of fittings?

Each elbow, tee, and valve adds resistance equal to a length of straight pipe. Adding that total equivalent length to the actual pipe length lets the friction formula account for all the fittings at once.

What pipe velocity should I target?

Keep velocity under roughly 5 ft/s on the suction side and 8 ft/s on the discharge to limit noise, erosion, and water hammer. The tool warns when velocity exceeds 8 ft/s so you can step up a pipe size.

Does TDH change with flow?

Yes. Static head is fixed, but friction and velocity head climb sharply with flow. That is why a pump and pipe are sized together as a system operating point, not in isolation.

What is the Pump Total Dynamic Head (TDH) Calculator?

Compute pump total dynamic head by summing static lift, Hazen-Williams friction loss with bundled C-factor tables, fitting losses as equivalent length, and velocity head. Built for plumbers and mechanical engineers selecting booster, transfer, and circulation pumps. It runs free in your browser on Gera Tools, with nothing uploaded.

Pump Total Dynamic Head (TDH) Calculator

Name: Pump Total Dynamic Head (TDH) Calculator
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

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Picking a pump is really about one number: total dynamic head. Get it wrong and the pump either starves the system or burns energy throttling against a needlessly oversized curve. This calculator builds TDH from its three real components.

How it works

TDH is the sum of static head, friction head, and velocity head. Friction uses the Hazen-Williams equation in US units:

hf per 100 ft = 0.2083 × (100 / C)^1.852 × Q^1.852 / d^4.8655
velocity (ft/s) = 0.4085 × Q / d²
velocity head   = velocity² / (2 × 32.174)
TDH = static head + friction head + velocity head

Here Q is flow in gpm, d is the inside diameter in inches, and C is the roughness coefficient (150 for PVC down to 100 for old steel). Fitting losses are folded in by adding their equivalent length to the pipe length.

Worked example

Moving 20 gpm through 150 ft of 1-inch Schedule 40 PVC (ID approximately 1.049 in, C = 150) with 30 ft of equivalent fittings against a 40 ft static lift:

Friction head over 180 ft effective length ≈ about 14 ft
Velocity at 20 gpm in 1.049-in pipe ≈ 7.4 ft/s
Velocity head ≈ 0.85 ft
TDH ≈ 40 + 14 + 0.85 ≈ 55 ft (illustrative — actual result depends on precise inputs)

For comparison, moving the same 20 gpm through 1.25-inch PVC (ID ≈ 1.364 in, C = 150) cuts friction loss to roughly 4 ft over the same run, dropping TDH to about 45 ft. That one pipe size change saves around 10 ft of head, which translates directly into a smaller, cheaper, quieter pump.

Pipe material and C-factor selection

Hazen-Williams C represents how smoothly a pipe conveys water. Selecting the right value matters:

Pipe material	Typical C
New PVC / HDPE	150
Copper or brass	130–140
New steel	120
Older steel / cast iron	100
Very old / tuberculated iron	80–90

Using C = 150 for old steel seriously underestimates friction loss; always base C on the pipe’s actual age and condition.

Velocity limits and their purpose

The velocity warning (flag at 8 ft/s discharge, 5 ft/s suction) protects hardware and comfort. Above 8 ft/s in copper or PVC, erosion-corrosion accelerates at fittings and elbows. Above 5 ft/s on the suction side, the drop in local pressure can cause cavitation: vapor bubbles that implode inside the pump impeller, eroding it rapidly and producing a distinctive rattling sound. The velocity head term is usually small — often under 1 ft — but it becomes meaningful in very high-velocity systems.

Reading the pump curve

TDH alone does not select a pump. You must plot your system curve — TDH at several flows — and find where it intersects the pump’s performance curve. The intersection is the actual operating point. An oversized pump will run to the right of its best efficiency point (BEP), drawing excess current and shortening seal and bearing life. The calculator gives you the design-flow TDH; check nearby flows too so you understand the system’s behavior across its range.