Total Dynamic Head Calculator

Easily calculate the Total Dynamic Head required for your pumping system.

Calculate Total Dynamic Head (TDH)

Summary of Inputs and Results

Parameter	Value	Unit
Static Head (H)	10.00	ft
Total Friction Losses (Hf)	5.00	ft
Velocity Head (Hv)	1.00	ft
Pressure Head Difference (Hp)	0.00	ft
Total Dynamic Head (TDH)	16.00	ft

Summary of TDH components based on your inputs.

What is Total Dynamic Head (TDH)?

Total Dynamic Head (TDH) is the total equivalent height that a fluid is to be pumped, taking into account elevation differences, friction losses in pipes and fittings, velocity of the fluid, and pressure differences. It represents the total amount of energy per unit weight that a pump must impart to the fluid to move it from the suction point to the discharge point under the specified conditions. TDH is typically expressed in units of length, such as feet or meters of the fluid being pumped.

The total dynamic head calculator is a crucial tool for engineers, system designers, and anyone involved in selecting and operating pumping systems. It helps determine the required pump capacity to overcome all resistances in the system and deliver the fluid to the desired location at the required pressure and flow rate.

Common misconceptions include confusing TDH with just the static elevation difference or neglecting friction losses and velocity head, which can lead to undersized pumps and system failure. The total dynamic head calculator accounts for all these factors.

Total Dynamic Head (TDH) Formula and Mathematical Explanation

The Total Dynamic Head (TDH) is the sum of several components of head, derived from the Bernoulli equation applied between the suction and discharge points of a pumping system:

TDH = H + Hf + Hv + Hp

Where:

• TDH = Total Dynamic Head
• H = Static Head (the difference in elevation between the discharge and suction free surfaces, Zd – Zs)
• Hf = Total Friction Losses (the sum of head losses due to friction in all pipes and fittings on both the suction and discharge sides)
• Hv = Velocity Head at the discharge (v²/2g, where v is the fluid velocity and g is the acceleration due to gravity – often considered at the discharge point as velocity at the free suction surface is negligible)
• Hp = Pressure Head Difference (the difference in pressure head between the discharge and suction surfaces, (Pd – Ps)/γ, where Pd and Ps are pressures and γ is the specific weight of the fluid)

Our total dynamic head calculator uses this fundamental formula.

Variables Table

Variable	Meaning	Unit	Typical Range
H	Static Head (Zd – Zs)	feet or meters	-100 to 500 ft (-30 to 150 m)
Hf	Total Friction Losses	feet or meters	0 to 100+ ft (0 to 30+ m)
Hv	Velocity Head (v²/2g)	feet or meters	0 to 10 ft (0 to 3 m)
Hp	Pressure Head Difference	feet or meters	-50 to 200 ft (-15 to 60 m)
TDH	Total Dynamic Head	feet or meters	Depends on system

Typical variable ranges for the total dynamic head calculator.

Practical Examples (Real-World Use Cases)

Example 1: Pumping Water from a Well to a Storage Tank

Imagine pumping water from a well where the water level is 50 ft below the pump centerline, to a storage tank where the water enters 20 ft above the pump centerline, and the tank is open to the atmosphere. The suction surface is at -50 ft relative to pump, discharge at +20 ft. Static head (H) = 20 – (-50) = 70 ft. Total friction losses (Hf) are estimated at 15 ft, and velocity head (Hv) at the discharge is 2 ft. Since both well and tank are open to atmosphere, Pressure Head Difference (Hp) is 0 ft.

Using the total dynamic head calculator inputs:

• Static Head (H): 70 ft
• Total Friction Losses (Hf): 15 ft
• Velocity Head (Hv): 2 ft
• Pressure Head Difference (Hp): 0 ft

TDH = 70 + 15 + 2 + 0 = 87 ft. A pump capable of delivering the required flow rate at 87 ft of head is needed.

Example 2: Circulating Fluid in a Closed Loop with Pressure Difference

Consider a closed-loop system where the fluid is circulated. The elevation difference between the highest and lowest points might be small, say Static Head (H) = 5 ft. However, there are significant friction losses (Hf) of 25 ft due to long pipes and fittings. Velocity head (Hv) is 1 ft. The pump is also overcoming a pressure differential, adding a Pressure Head Difference (Hp) of 10 ft.

Using the total dynamic head calculator inputs:

• Static Head (H): 5 ft
• Total Friction Losses (Hf): 25 ft
• Velocity Head (Hv): 1 ft
• Pressure Head Difference (Hp): 10 ft

TDH = 5 + 25 + 1 + 10 = 41 ft. The circulation pump needs to provide 41 ft of head at the design flow rate.

How to Use This Total Dynamic Head Calculator

1. Select Units: Choose whether you are working in ‘Feet’ or ‘Meters’. All head and loss inputs should be in the selected unit.
2. Enter Static Head (H): Input the vertical elevation difference between the discharge and suction free surfaces. If discharge is above suction, it’s positive.
3. Enter Total Friction Losses (Hf): Input the sum of all head losses due to friction in pipes, valves, and fittings in both suction and discharge lines. You might need a separate friction loss calculator for this.
4. Enter Velocity Head (Hv): Input the velocity head (v²/2g) at the point of discharge or where TDH is being evaluated.
5. Enter Pressure Head Difference (Hp): Input the difference in pressure head between the discharge and suction conditions.
6. View Results: The calculator automatically updates the Total Dynamic Head (TDH) and its components, displayed in the results section, chart, and table.
7. Interpret Results: The calculated TDH is the head the pump must generate at the desired flow rate. Use this value to select a suitable pump by comparing it against pump performance curves.

Key Factors That Affect Total Dynamic Head (TDH) Results

• Elevation Difference (Static Head): The greater the vertical distance the fluid is lifted, the higher the TDH.
• Pipe Roughness and Diameter: Smoother and larger diameter pipes reduce friction losses, lowering TDH.
• Flow Rate: Higher flow rates increase velocity head and friction losses significantly, thus increasing TDH.
• Pipe Length and Fittings: Longer pipes and more fittings (bends, valves) increase friction losses and TDH.
• Fluid Viscosity and Density: More viscous fluids or denser fluids can increase friction losses (though density also affects pressure head conversion). Our calculator assumes water or similar fluid unless pressure head is directly provided.
• System Pressures: Differences in pressure at the suction and discharge points directly contribute to the TDH via the pressure head component.

Frequently Asked Questions (FAQ)

What is the difference between static head and total dynamic head?

Static head is only the vertical elevation difference between the source and destination free surfaces. Total Dynamic Head (TDH) includes static head plus all losses (friction), velocity head, and any pressure head differences.

Why is TDH important for pump selection?

Pumps are rated by their ability to deliver a certain flow rate against a specific head (TDH). You need to calculate the system’s TDH at the desired flow rate to select a pump that can meet those requirements efficiently, as shown on pump curves.

How do I calculate friction losses (Hf)?

Friction losses are calculated using formulas like Darcy-Weisbach or Hazen-Williams, considering pipe material, diameter, length, flow rate, and fittings. You can use a dedicated friction loss calculator for this.

What if my suction is from a pressurized tank?

If the suction tank is pressurized, the suction pressure (Ps) will be higher, leading to a positive suction pressure head (Hps), which reduces the TDH compared to an open tank at the same elevation.

What if I am discharging to a pressurized tank?

If discharging to a pressurized tank, the discharge pressure (Pd) is higher, increasing the pressure head difference (Hp) and thus the TDH.

Is velocity head always small?

In many systems with large pipes and moderate velocities, velocity head can be relatively small compared to static head and friction losses. However, in systems with high velocities, it becomes significant and must be included in the total dynamic head calculator.

Does the total dynamic head calculator work for any fluid?

The calculator itself sums head components. However, friction losses (Hf) and the conversion from pressure to pressure head (Hp) depend on fluid properties (density and viscosity). If you input Hf and Hp directly in units of head of the fluid, it works. If calculating Hf or Hp from pressure and fluid properties, those properties matter greatly. See our fluid dynamics basics page.

What happens if the pump head is less than the TDH?

If the pump cannot provide the required TDH at the desired flow rate, the actual flow rate will be lower than desired, or the pump may not be able to deliver fluid at all if the TDH is significantly underestimated.