Pipe pressure drop calculator
Friction pressure loss in a straight pipe plus fittings, using Darcy–Weisbach with the Swamee–Jain friction factor. Defaults are water at 20 °C.
Velocity · Reynolds—
Friction factor—
Pressure drop—
Typical K values: 90° LR elbow 0.3, tee through 0.4, tee branch 1.0, gate valve open 0.15, globe valve 6, swing check 2, entrance 0.5, exit 1.0.
Method
ΔP = (f·L/D + ΣK) · ρv²/2. Laminar flow (Re < 2300): f = 64/Re. Turbulent: f = 0.25 / [log₁₀(ε/3.7D + 5.74/Re⁰·⁹)]².
Frequently asked questions
What is a typical pressure drop for water piping?
Designers often aim for roughly 0.5–2 bar per 100 m in pumped water lines, balancing pump energy against pipe cost.
What roughness should I use for steel pipe?
About 0.045 mm for new commercial steel; 0.015 mm for stainless; more for old or corroded pipe.
Last updated 2026-11-02