About the Pressure Drop Calculator
What is the Pressure Drop Calculator?
Friction along a pipe and in its fittings reduces pressure. This pressure drop calculator uses the Darcy–Weisbach equation, with the friction factor from the Swamee–Jain approximation of the Colebrook equation.
Add the loss coefficients (K) of elbows, tees and valves to include fitting losses.
How to use the Pressure Drop Calculator
- Water Flow (L/min) (sample: 300)
- Pipe Inner Diameter (mm) (sample: 50)
- Pipe Length (m) (sample: 100)
- Pipe Material (sample: PVC / CPVC / HDPE (0.0015 mm))
- Sum of Fitting Loss Coefficients (K) (sample: 5)
- Press Calculate Pressure Drop (results also refresh as you type). The result card shows the Pressure Drop, along with Head loss, Pipe friction loss, Fitting losses and Velocity.
Formula used
h = f × (L ÷ D) × v² ÷ 2g + ΣK × v² ÷ 2g
- f (turbulent) = 0.25 ÷ [log₁₀(ε ÷ 3.7D + 5.74 ÷ Re^0.9)]²
- f (laminar) = 64 ÷ Re
- Pressure = ΔP = ρ × g × h
10 m of head loss is about 1 bar for water.
Worked example
These are the sample values already filled in the calculator above, and the result it returns for them:
| Input | Sample value |
|---|---|
| Water Flow (L/min) | 300 |
| Pipe Inner Diameter (mm) | 50 |
| Pipe Length (m) | 100 |
| Pipe Material | PVC / CPVC / HDPE (0.0015 mm) |
| Sum of Fitting Loss Coefficients (K) | 5 |
| Result | Value |
|---|---|
| Pressure Drop | 1.276 bar |
| Head loss | 13.04 m |
| Pipe friction loss | 11.38 m |
| Fitting losses | 1.65 m |
| Velocity | 2.546 m/s |
| Friction factor | 0.0172 |
| Reynolds number | 1,26,817 |
Tips for using the Pressure Drop Calculator
- Pressure drop rises with the square of velocity – a slightly larger pipe cuts losses sharply.
- Old steel and GI pipes become rougher with scale; allow extra margin.