Net Head Calculator

Enter project inputs

All heads are computed in meters of fluid.

Defaults are provided for quick testing.

Upstream elevation z1 (m)

Downstream elevation z2 (m)

Upstream pressure p1 (kPa, gauge)

Downstream pressure p2 (kPa, gauge)

Upstream diameter d1 (m)

Downstream diameter d2 (m)

Pipe length L (m)

Flow rate Q (m³/s)

Friction factor f (Darcy)

Typical range: 0.01–0.06 (varies by pipe and Reynolds number).

Minor loss sum K

Sum of fittings, valves, entrances, bends, and exits.

Fluid density ρ (kg/m³)

Gravity g (m/s²)

Reset

Formula used

The calculator treats point 1 as upstream and point 2 as downstream. Net head is the gross available head minus hydraulic losses.

Head components

Static head = z1 − z2
Pressure head = (P1 − P2) / (ρ g)
Velocity head = (V1² − V2²) / (2 g)
Gross head = Static + Pressure + Velocity

Losses

V = Q / A, where A = π D² / 4
hf = f (L/D) (V² / (2 g))
hm = K (V² / (2 g))
Net head = Gross head − (hf + hm)
Power = ρ g Q Hnet

If you use gauge pressures at both points, keep both consistent. For open channels, set p1 and p2 to zero.

How to use this calculator

Enter upstream and downstream elevations from the same datum.
Add pressures if points are in pressurized flow conditions.
Provide diameters at each point to compute velocities accurately.
Enter pipe length, flow rate, friction factor, and summed minor losses.
Click calculate to view net head and power estimate above.
Download CSV or PDF to store a calculation record.

Example data table

Scenario	z1 (m)	z2 (m)	Q (m³/s)	D (m)	L (m)	f	K	Net head (m)
Hydropower penstock	120	85	0.45	0.60	350	0.02	3.5	≈ 28.9
Short pipeline transfer	55	48	0.15	0.40	120	0.03	2.0	≈ 4.5
Open channel drop	30	20	0.08	0.30	80	0.04	1.2	≈ 8.3

Values are illustrative. Use project-specific friction and minor losses for design.

Design intent for net head studies

Net head represents the useful energy per unit weight delivered between two reference points after accounting for losses. In construction projects, it supports pump selection, turbine feasibility checks, and verification of hydraulic grade line targets. A reliable estimate reduces rework by aligning civil elevations, pipe routing, and equipment envelopes with expected operating conditions. It also improves bid accuracy by linking mechanical loads to realistic site geometry.

Inputs that control gross head

Gross head is driven mainly by elevation difference, plus any upstream or downstream pressure contribution. When points are vented to atmosphere, gauge pressures are near zero and elevation becomes dominant. In closed systems, pressure head can offset elevation and may reverse flow if downstream pressure exceeds upstream pressure. Velocity head differences matter when diameters change or when velocities are high.

Loss modeling for pipelines and fittings

Friction loss depends on friction factor, length, diameter, and velocity. Small diameter reductions can increase velocity sharply, raising losses and lowering available net head. Minor losses capture entrances, valves, bends, reducers, and outlets through the summed K value. Using a realistic K improves agreement between calculations and commissioning measurements. Segment routes for checks.

Interpreting results for equipment sizing

Compare net head to the required head at the design flow from pump curves or turbine specifications. A positive margin is recommended to cover tolerances, aging, and seasonal changes. If net head is low, options include reducing flow, increasing diameter, shortening runs, smoothing fittings, or revising elevations during earthworks. If net head is high, confirm pressure ratings, thrust blocks, and surge protection allowances.

Documentation and field verification

Exported reports help communicate assumptions to stakeholders and support change control. During construction, verify datum elevations, confirm pipe internal diameter, and document valve and fitting counts for the final K estimate. After startup, compare measured pressure and flow to the report to refine friction and minor loss assumptions for future phases. Maintain a calibration log so future upgrades start from verified parameters.

FAQs

1) What is the difference between gross head and net head?

Gross head combines elevation, pressure, and velocity effects between two points. Net head subtracts friction and minor losses, giving the usable head available to a pump or turbine.

2) Which pressure should I enter, absolute or gauge?

Use gauge pressure for both points so the reference cancels consistently. If both points are open to atmosphere, set pressures to zero and rely on elevation and losses.

3) How do I estimate the friction factor f?

For preliminary work, choose a typical value based on pipe material and expected Reynolds number. For detailed design, derive f from a Moody chart or calibrated field data for your pipeline.

4) How do I build the minor loss coefficient K?

Sum K values for each fitting, valve, entrance, reducer, bend, and exit on the flow path. Manufacturer data and standard tables are commonly used during design and refined during as-built verification.

5) Why can net head become negative?

Negative net head means losses and opposing pressure or elevation exceed the driving head for the assumed flow direction. Recheck point selection, elevations, pressures, and whether downstream conditions dominate.

6) Can I use this for open-channel conditions?

Yes, for a quick estimate. Set pressures to zero, confirm the chosen diameters represent hydraulic sections, and treat computed losses as an approximation. For final design, use a dedicated open-channel method.