How to Calculate Total Dynamic Head

Total Dynamic Head (TDH) Calculator

Static Suction Lift/Head (ft) Vertical distance from water level to pump (positive for lift, negative for head).

Static Discharge Head (ft) Vertical distance from pump to highest discharge point.

Friction Loss (Pipes/Fittings) (ft) Resistance caused by pipe length, elbows, and valves.

Operating Pressure (PSI) Pressure required at the end of the line (e.g., nozzle pressure).

Result: 0 feet

Static Head: 0 ft
Friction Head: 0 ft
Pressure Head: 0 ft

function calculateTDH() { var suction = parseFloat(document.getElementById('suctionHead').value) || 0; var discharge = parseFloat(document.getElementById('dischargeHead').value) || 0; var friction = parseFloat(document.getElementById('frictionLoss').value) || 0; var psi = parseFloat(document.getElementById('systemPressure').value) || 0; // Calculation Logic // 1 PSI = 2.31 feet of head var pressureHead = psi * 2.31; var staticHead = suction + discharge; var totalDynamicHead = staticHead + friction + pressureHead; document.getElementById('tdhResultValue').innerText = totalDynamicHead.toFixed(2); document.getElementById('staticHeadBreakdown').innerText = staticHead.toFixed(2); document.getElementById('frictionHeadBreakdown').innerText = friction.toFixed(2); document.getElementById('pressureHeadBreakdown').innerText = pressureHead.toFixed(2); document.getElementById('tdh-result-box').style.display = 'block'; }

Understanding Total Dynamic Head (TDH)

Total Dynamic Head (TDH) is the total equivalent height that a fluid must be pumped, taking into account friction losses, elevation changes, and pressure requirements. It is the most critical metric used when selecting a pump, as it determines how much work the pump must perform to move a specific volume of liquid through a piping system.

The TDH Formula

To calculate TDH, you use the following primary components:

TDH = Static Head + Friction Loss + Pressure Head

1. Static Head

Static Head represents the vertical distance the water must travel. It consists of two parts:

Static Suction Lift/Head: The vertical distance from the water source to the pump. If the pump is above the water, this is "lift." If the pump is below the water source, this is "positive suction head" (which reduces the work the pump has to do).
Static Discharge Head: The vertical distance from the pump center line to the highest point in the discharge piping.

2. Friction Loss

As water flows through pipes and fittings (elbows, tees, valves), it rubs against the walls and creates turbulence. This energy loss is called friction loss. It depends on the pipe material, diameter, length, and the flow rate (GPM). Most engineers use the Hazen-Williams formula or standard friction loss tables to determine this value.

3. Pressure Head

If your system requires a specific pressure at the end of the line (such as a sprinkler head needing 30 PSI to function), you must convert that pressure into feet of head. The conversion factor is 1 PSI = 2.31 Feet of Head.

Example Calculation

Suppose you are installing a residential well pump with the following parameters:

Vertical lift from well: 10 feet
Vertical height to tank: 40 feet
Friction loss in pipes: 12 feet
Required tank pressure: 40 PSI

Step 1: Calculate Static Head: 10 ft + 40 ft = 50 ft

Step 2: Calculate Pressure Head: 40 PSI × 2.31 = 92.4 ft

Step 3: Sum everything: 50 (Static) + 12 (Friction) + 92.4 (Pressure) = 154.4 feet TDH.

Using this TDH value along with your desired Gallons Per Minute (GPM), you can consult a pump curve to select the most efficient motor for your application.