Energy Grade Line Calculator

Model heads, losses, flow, and section conditions. See EGL and HGL changes across the pipeline. Download results, study formulas, and plot profiles with confidence.

Calculator Inputs

Enter values for elevations, pressures, diameters, flow, losses, and added or extracted head.

Pipe Length (m)

Upstream Elevation z1 (m)

Downstream Elevation z2 (m)

Upstream Gauge Pressure p1 (kPa)

Measured Downstream Gauge Pressure p2 (kPa)

Flow Rate Q (m³/s)

Upstream Diameter D1 (m)

Downstream Diameter D2 (m)

Kinetic Correction α1

Kinetic Correction α2

Friction Head Loss hf (m)

Minor Head Loss hm (m)

Pump Head Added hp (m)

Turbine Head Removed ht (m)

Specific Weight γ (N/m³)

Gravity g (m/s²)

Example Data Table

This sample helps verify the calculator workflow before using project values.

Item	Sample Value	Meaning
Pipe Length	120 m	Distance between upstream and downstream sections.
z1 / z2	18 m / 10 m	Section elevations above the chosen datum.
p1 / p2	185 kPa / 125 kPa	Measured gauge pressures at both sections.
Q	0.18 m³/s	Volumetric flow rate through the line.
D1 / D2	0.30 m / 0.25 m	Section diameters used for velocity calculation.
hf + hm	6.0 m	Total head loss from friction and fittings.
Expected Use	EGL and HGL check	Compare theoretical and measured energy conditions.

Formula Used

1) Velocity

A = πD² / 4

V = Q / A

2) Pressure Head

Pressure Head = p / γ

In this file, pressure is entered in kPa, so the code converts it to Pa before dividing by specific weight.

3) Hydraulic Grade Line

HGL = z + p/γ

The hydraulic grade line contains elevation head and pressure head only.

4) Energy Grade Line

EGL = z + p/γ + αV²/(2g)

The energy grade line equals the hydraulic grade line plus velocity head.

5) Extended Energy Equation

EGL₂ = EGL₁ + h_p - h_t - h_f - h_m

This relation estimates the downstream energy state after added head and losses.

How to Use This Calculator

Enter the upstream and downstream elevations relative to one datum.
Provide gauge pressures in kPa for both sections.
Enter flow rate and section diameters to calculate velocity heads.
Insert friction loss, minor loss, pump head, and turbine head.
Adjust specific weight and gravity if the fluid is not standard water.
Submit the form to show results above the calculator.
Review the table, compare theoretical and measured values, then export CSV or PDF.
Use the Plotly chart to inspect EGL, HGL, and elevation trends.

FAQs

1) What does the energy grade line represent?

The energy grade line shows the total head available at a section. It combines elevation head, pressure head, and velocity head into one engineering profile.

2) How is HGL different from EGL?

HGL includes only elevation and pressure head. EGL sits above HGL by the velocity head amount, unless flow velocity is zero.

3) Why enter both measured and theoretical downstream conditions?

The calculator compares a measured downstream pressure with the theoretical energy equation result. This helps identify mismatch, missing losses, or instrumentation issues.

4) What does a negative required downstream pressure mean?

A negative gauge pressure means the line would need sub-atmospheric pressure at the downstream section to satisfy the stated flow and losses.

5) Can I use fluids other than water?

Yes. Replace the specific weight value with the correct fluid specific weight. That updates pressure head and all head-based comparisons.

6) Why are kinetic energy correction factors included?

The α factor improves accuracy when the velocity profile is nonuniform. For many engineering estimates, α is set near 1.0.

7) Does this calculator size the pipe for me?

No. It evaluates head conditions from the values you enter. It is best used for checking profile behavior and energy balance.

8) What does the energy balance residual show?

The residual measures the gap between the theoretical energy equation and the measured downstream state. A value near zero indicates good agreement.