Pipe Pressure Drop Calculator
Find total pressure drop across a pipe run — straight-pipe friction loss plus fitting losses — from flow rate, pipe geometry, roughness, and a combined fitting K-factor.
Enter your values
Pipe run, fluid properties, and fittings.
How this calculator works
Straight-pipe friction loss follows the Darcy-Weisbach equation:
Fittings, valves, and bends add further loss proportional to velocity head, summed as a single K-factor:
The friction factor f is found from the Reynolds number: f = 64/Re for laminar flow (Re < 2300), or the Swamee-Jain approximation for turbulent flow, which accounts for relative pipe roughness. Total pressure drop is the sum of both terms.
Typical fitting K-factors
| Fitting | Typical K |
|---|---|
| 90° standard elbow | 0.75 – 0.9 |
| 45° elbow | 0.35 – 0.45 |
| Gate valve (full open) | 0.15 – 0.2 |
| Globe valve (full open) | 6 – 10 |
| Tee, flow through run | 0.3 – 0.4 |
Add up the K-values for every fitting in the run and enter the total. These are general reference values — use manufacturer data where precision matters.
Frequently asked questions
What roughness value should I use?
Common steel pipe uses ~0.045 mm, PVC and drawn copper are much smoother (~0.0015 mm), and older or corroded pipe can be significantly rougher. Use the manufacturer's value where available.
Does this include elevation change?
No — this calculates friction and fitting losses only. If the pipe run also rises or falls, add the static head (ρ·g·Δz) separately to get total system pressure difference.