Hydraulic Head Calculator

Enter values and calculate hydraulic head

Sample inputs and results

Total hydraulic head from Bernoulli terms

The hydraulic head at a point combines three energy terms per unit weight: elevation head, pressure head, and velocity head.

• z is elevation above the chosen datum (m).
• p/(ρg) is pressure head (m of fluid).
• v²/(2g) is velocity head (m of fluid).
• H is total head, often used for energy comparisons.

Steps for accurate head calculations

1. Enter density and gravity for your fluid and location.
2. Provide pressure, velocity, and elevation for point 1.
3. Choose units from each dropdown, then calculate.
4. Enable the second point to compute head difference ΔH.
5. Export results using the CSV or PDF buttons if needed.

Hydraulic head for design, diagnostics, and reporting

1) What hydraulic head represents

Hydraulic head is the mechanical energy of a fluid per unit weight, written in meters of fluid. It combines elevation, pressure, and velocity into one comparable number for flow systems. Engineers use head to track where energy is available, added, or dissipated.

2) Pressure head conversion benchmarks

Pressure head is p/(ρg). For water near 20°C (ρ ≈ 1000 kg/m³) and standard gravity, 1 bar equals about 10.2 m of water head, while 100 kPa corresponds to roughly 10.2 m as well. A household supply of 200–500 kPa is commonly 20–50 m of head.

3) Velocity head and when it matters

Velocity head v²/(2g) becomes important in smaller pipes, nozzles, and high-speed lines. For example, v = 3 m/s gives a velocity head of about 0.46 m, while v = 10 m/s gives about 5.10 m. In reservoirs and large tanks, velocity is near zero and this term can be neglected.

4) Elevation head and datums

Elevation head z depends on your chosen reference level (datum). The datum can be sea level, a plant benchmark, or a local floor. Consistency is the key: head comparisons only make sense when both points use the same datum.

5) Comparing two points to interpret losses

When you enable point comparison, the calculator reports ΔH = H₁ − H₂. In a real pipe, a drop in total head often indicates losses from friction, fittings, valves, and entrances. Large positive ΔH over a short distance is a strong signal to check roughness, blockage, or a partially closed valve.

6) Groundwater and piezometric head

In groundwater, velocity head is usually tiny compared to pressure and elevation. The common quantity is piezometric head, z + p/(ρg), which drives flow from higher head to lower head. Typical aquifer gradients can be small, such as 0.001–0.01 m/m, yet still produce meaningful discharge over long distances.

7) Pumps, turbines, and energy accounting

Pumps add head; turbines remove it. Across a pump, the rise in total head approximates the pump head delivered to the fluid. For reporting, engineers often present suction and discharge heads, then compare the difference to expected performance curves.

8) Field measurement tips

Use stable units, document the datum, and note whether pressure is gauge or absolute. If using absolute pressure sensors, enable the atmospheric option for consistent head terms. Exporting CSV or PDF helps maintain traceable calculations in audits.

Frequently asked questions

1) Should I enter gauge or absolute pressure?

Enter gauge pressure in most piping work. If your instrument reports absolute pressure, enable the atmospheric option so pressure head is computed consistently for both points.

2) When can I set velocity to zero?

Set velocity to zero for large reservoirs, calm tanks, or free surfaces where flow speed is negligible compared with pipe velocities. This removes the velocity head term.

3) Can hydraulic head be negative?

Yes. If elevation is below the chosen datum or gauge pressure is below atmospheric, the summed head can be negative. The sign depends on your reference and measurement basis.

4) What density should I use for oils or brines?

Use the fluid density at operating temperature. Light oils may be 800–900 kg/m³, while brines can exceed 1100 kg/m³. Density directly scales pressure head.

5) Why must both points use the same elevation datum?

Because ΔH uses the difference between total heads. If the elevation references differ, you introduce an artificial offset that looks like a gain or loss that is not real.

6) Does ΔH equal head loss in a pipe?

Often, yes, when no pump or turbine lies between the two points and flow is steady. If a pump adds energy, ΔH includes both the added head and the losses.

7) How do I convert kPa to meters of water head quickly?

For water, 100 kPa is about 10.2 m of head under standard gravity. A quick estimate is head (m) ≈ pressure (kPa) ÷ 9.81.

Practical guidance

• Use gauge pressures unless your workflow requires absolute values.
• Keep the same datum for both elevations when comparing points.
• In open-channel flow, pressure head is near zero at the surface.
• For compressible fluids, the simple form can be an approximation.

Use it wisely to compare systems and reduce losses.