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.

Pump Total Dynamic Head (TDH) Calculator

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.

Example and tips

Moving 20 gpm through 150 ft of 1-inch copper (ID 1.025) with 30 ft of equivalent fittings against a 40 ft static lift gives a friction loss of a few feet on top of the 40 ft static, for a TDH near the low-40s. Because friction scales with the 1.85 power of flow, the single biggest lever is pipe diameter: bumping up one size can halve the friction term. Always read the pump curve at your design flow, not just the shut-off head.