Enter suction & discharge heads, pipe friction losses, flow rate, and required discharge pressure to get the Total Dynamic Head, velocity head, and pump power needed for correct pump selection.
Fill in the head, friction, and flow details of your pumping system below.
Pump is mounted above the water source, so it must lift water up to itself.
Velocity Head (from flow & pipe size)
Used to estimate velocity head (usually small, but included for accuracy per Hydraulic Institute practice).
Head required at rated flow for pump selection
Enter your values and hit calculate to see a pump selection summary.
Total Dynamic Head is the single most important number when selecting a centrifugal pump for any application — water supply, irrigation, drainage, firefighting, or industrial process water. Pump manufacturers publish a head-versus-flow performance curve for every model, and TDH is the value you match against that curve at your required flow rate. Get TDH wrong and the pump will either deliver far less flow than expected once it fights real system resistance, or it will run oversized and inefficient off its best-efficiency point — both the Pumps & Systems trade literature and the Hydraulic Institute's pump standards treat accurate TDH calculation as the starting point of any pump selection exercise.
TDH is built from four components in this calculator. The static head is the net vertical lift between the water source and the discharge point. If the pump sits above the water level, it has to overcome a suction lift, which adds directly to the head the pump must supply. If instead the source is above the pump (flooded suction, common on tanks and sumps feeding a pump below them), that head actually assists the pump and is subtracted: Static Head = Discharge Head + Suction Lift or Static Head = Discharge Head − Suction Head (flooded).
The friction loss accounts for energy lost to resistance inside the pipework — pipe wall roughness, bends, valves, strainers, and fittings on both the suction and discharge runs. This loss grows roughly with the square of flow velocity, which is why oversizing a pipe by even one size can meaningfully cut friction head, a relationship explained in detail by resources such as the Engineering ToolBox friction loss references and the classic Hazen-Williams and Darcy-Weisbach equations used industry-wide. In the field, friction loss is usually taken from pipe friction charts or pump-house hydraulic calculations for the pipe size, length, and fittings involved, then entered directly here.
The velocity head represents the kinetic energy of the moving fluid at the discharge point, calculated as hv = V² ÷ (2 × g), where V is flow velocity in m/s (from flow rate ÷ pipe cross-sectional area) and g is 9.81 m/s². Velocity head is usually small for typical pipe velocities of 1–3 m/s but is included here for completeness, consistent with the full energy-balance form of the pump head equation covered in standard fluid mechanics references such as Cengel & Cimbala's Fluid Mechanics: Fundamentals and Applications.
Finally, if the pump must discharge into a pressurized vessel, boiler, or pressurized irrigation line rather than simply to atmosphere, that required pressure head is added by converting the pressure rating to an equivalent head of water, using the standard conversion of 1 bar ≈ 10.2 m of water head. Adding all four terms gives the final TDH: TDH = Static Head + Total Friction Loss + Velocity Head + Pressure Head.
Once TDH and flow rate are known, the hydraulic power the pump must impart to the fluid is P(kW) = (Q × H × ρ × g) ÷ 3,600,000, with Q in m³/hr, H in metres, and ρ = 1000 kg/m³ for water. Dividing by the pump's overall efficiency gives the shaft power the driving motor must supply — this figure, along with TDH and flow, is what you hand to a pump supplier or use to size the driving motor.
As with any sizing calculator, treat the result as an engineering starting point. Site-specific pipe condition, actual fitting counts, water temperature, and elevation changes over the pump's service life all shift the real-world number, so always confirm final TDH against as-built pipe layouts and verify the selected pump's published curve before purchase and installation.
Static head is only the physical elevation difference between the source and destination. TDH adds friction losses, velocity head, and any required discharge pressure on top of static head, giving the true total resistance the pump must overcome — which is why TDH, not static head alone, is used to select a pump from its performance curve.
Suction lift means the pump is mounted above the water source, so it must draw water upward before it even reaches the impeller — this adds to the head the pump must supply and increases the risk of cavitation if the lift is excessive. Flooded suction means the water source is above the pump (gravity-fed), which assists the pump and is subtracted from the total head requirement.
Friction loss depends on pipe diameter, length, interior roughness, flow velocity, and the number of bends, valves, and fittings. Standard friction-loss charts (Hazen-Williams or Darcy-Weisbach based) published by pipe manufacturers and engineering references give loss per 100 m of pipe for a given diameter and flow rate; multiply by your actual pipe length and add an allowance of roughly 10–20% for fittings if you don't have an exact fitting count.
Velocity head scales with the square of velocity divided by twice gravitational acceleration. At typical design velocities of 1–3 m/s in pipework, this works out to only a few centimetres of head, which is why it is often neglected in quick hand calculations — but it is retained here for completeness and becomes more significant in smaller, high-velocity pipe runs.
Take the calculated TDH and your required flow rate, then find a pump whose published head-versus-flow performance curve passes through or above that point, ideally close to its best efficiency point (BEP) rather than at the extreme ends of the curve. Use the shaft power figure to confirm the driving motor is rated with adequate margin above that requirement.