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Pumps & Rotating Equipment

Total Dynamic Head Calculator

Total dynamic head (TDH) is the total head a pump must add to the system to move the duty flow against the elevation/static-pressure difference between suction and discharge and to overcome the friction and minor losses around the circuit. This calculator builds TDH transparently from its components — static elevation difference, the net pressure-head contribution, pipe friction losses, fitting/minor losses, and an optional velocity-head change — and then applies a design allowance to give a design TDH. Two modes let you work the way your data arrives: pressure terms, where suction and discharge gauge pressures are converted to head with H = ΔP/(ρ·g); or head terms, where you enter the suction and discharge pressure heads directly. Every term is an explicit, editable input — there are no hidden defaults — so the result is a preliminary, fully auditable estimate of the system-side head. It is the head the pump curve must meet at the duty flow; the pump curve itself comes from the vendor. TDH here is a preliminary sizing estimate only: it is not a pump selection, not a vendor-curve replacement, not a pipe-network solver, and not a transient/surge analysis.

TypeInteractive engineering calculator

Calculator

Static elevation
m

+ discharge above suction, − discharge below

Suction & discharge (gauge pressures)
kg/m³
kPa
kPa
m/s²

Standard gravity (editable)

System losses
m

Straight-pipe (major) loss — use Pipe Head Loss / Darcy-Weisbach

m

Fittings & valves — use Minor Loss / K-Value

m

Usually small; enter 0 if suction and discharge velocities are similar

%

Preliminary margin on the computed TDH

Static / elevation head15 m
Pressure head contribution20.3943 m
Friction losses8 m
Minor losses2 m
Velocity head contribution0 m
Base TDH45.3943 m
Design TDH (with allowance)49.9338 m

Preliminary system-side head estimate only. Not pump selection, not a guaranteed duty point, not a vendor pump-curve replacement, not a pipe-network solver, and not a transient/surge analysis. Final design requires a verified hydraulic profile, line list, fittings, control-valve losses, operating cases, vendor pump curves, project/client standards, and qualified engineering review.

Related: Pump Sizing · System Curve vs Pump Curve · Head ↔ Pressure · Pipe Head Loss · Minor Loss · NPSH Available

Formulas

Pressure head from ΔP
H = ΔP / (ρ · g)
TDH — pressure terms
TDH = z_static + (P_dis − P_suc)/(ρ·g) + H_friction + H_minor + H_velocity
TDH — head terms
TDH = z_static + H_dis_head − H_suc_head + H_friction + H_minor + H_velocity
Design TDH
TDH_design = TDH × (1 + allowance / 100)

Diagram

suctiondischargez_staticH_friction + H_minorTDH = z_static+ ΔP/(ρg)+ losses + H_v

Worked example

Water (1000 kg/m³) is pumped with a 15 m static elevation difference. Suction gauge pressure is 0 kPa and discharge gauge pressure is 200 kPa; friction losses are 8 m, minor losses 2 m, and the velocity-head change is negligible. Apply a 10% design allowance (pressure-terms mode, g = 9.80665 m/s²).

  1. 01Pressure head = (200 − 0) × 1000 / (1000 × 9.80665) = 200000 / 9806.65 = 20.39 m
  2. 02Base TDH = 15 + 20.39 + 8 + 2 + 0 = 45.39 m
  3. 03Design TDH = 45.39 × (1 + 10/100) = 45.39 × 1.10
  4. 04Design TDH = 49.93 m
Result

Base TDH ≈ 45.39 m; design TDH ≈ 49.93 m. Meet this against a vendor pump curve at the duty flow and confirm the NPSH margin before selection.

FAQ

What is total dynamic head (TDH)?
TDH is the total head a pump must add to the system at the duty flow: the static elevation difference, plus the net pressure-head difference between suction and discharge, plus all friction and minor (fitting) losses, plus any velocity-head change. It is the head the pump curve has to meet — the system side of the duty point.
What is the difference between static head and TDH?
Static head is only the elevation (and any pressure) difference the pump must overcome at zero flow. TDH adds the flow-dependent friction and minor losses on top of the static component, so TDH rises with flow while static head does not. Sizing on static head alone understates the head the pump actually needs.
Should I use pressure terms or head terms?
Use whichever matches your data. Pressure terms take suction and discharge gauge pressures and convert their difference to head with H = ΔP/(ρ·g), which needs the fluid density. Head terms take the suction and discharge pressure heads directly. Both produce the same TDH for consistent inputs.
How do I get the friction and minor loss values?
Estimate them separately and enter them as positive heads. Use the Pipe Head Loss or Darcy-Weisbach calculator for straight-pipe friction and the Minor Loss / K-Value calculator for fittings and valves, then sum them into the friction and minor-loss inputs here.
What design allowance should I apply?
The allowance is a preliminary margin on the computed TDH to cover uncertainty in losses, fouling, and future duty changes. A modest allowance is common at the estimate stage, but the right value depends on project standards, the confidence in the loss estimates, and the service. It is not a substitute for proper operating-case analysis.
Is TDH enough to select a pump?
No. TDH is the preliminary system-side head only. Final selection requires the vendor pump curve and NPSHr at the duty flow, an NPSH-available check, materials for the service, operating cases, and qualified engineering review. This calculator is not a vendor-curve replacement, a pipe-network solver, or a surge analysis.

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