Darcy-Weisbach Head Loss Calculator
Friction head loss and pressure drop along a pipe, with the flow rate and the power it costs.
Results
Head loss
4.0789
m
Pressure
39.920
kPa
Head loss
4.0789
m
Flow rate
14.137
m³/h
Power
0.1568
kW
What this tool does
Head loss goes with the square of the velocity and inversely with the diameter, so a pipe one size up is often cheaper over its life than the pumping energy the smaller one wastes. The minor loss coefficient is the sum of the K values for bends, valves and fittings on the run — a standard elbow is around 0.3 and a fully open gate valve around 0.2, but take them from the fitting data. Get the friction factor from the Reynolds number calculator.
Formula
hf = f × (L ÷ D) × v² ÷ (2g)
Variables
| Symbol | Meaning | Unit |
|---|---|---|
ff | Friction factor | — |
lp | Pipe length | m |
dd | Pipe diameter | mm |
vv | Speed | m/s |
ro | Fluid density | kg/m³ |
kl | Sum of minor loss coefficients | — |
HF | Head loss | m |
DP | Pressure | kPa |
HM | Head loss | m |
QQ | Flow rate | m³/h |
PW | Power | kW |
Worked example
- Friction factor0.02
- Pipe length50 m
- Pipe diameter50 mm
- Speed2 m/s
- Fluid density998 kg/m³
- Sum of minor loss coefficients0
- Head loss4.0789 m
- Pressure39.920 kPa
- Head loss4.0789 m
- Flow rate14.137 m³/h
- Power0.1568 kW
Limitations
- The formula assumes ideal conditions: no friction losses, no air resistance and no efficiency losses unless you enter them.
- For work that must comply with a standard or be signed off, check the result against the applicable code and have it reviewed by a qualified engineer.
- Mixing units is the most common source of error. Convert every input to the units shown next to each field before calculating.