What is the difference between Darcy and Fanning friction factors?

The Darcy friction factor is 4 times the Fanning friction factor. Make sure the equation you are using expects the correct one. The Darcy–Weisbach equation uses the Darcy friction factor.

Do I need to account for minor losses?

Yes, in real systems you should always include them by using the K-value of each fitting and adding it as equivalent length or additional ΔP.

Live

Piping

Pressure Drop Calculator

Estimate frictional pressure loss along a pipe using the Darcy–Weisbach equation.

When to use this calculator

Use for hydraulic checks, pump sizing, and verifying line pressure budgets.

Required inputs

Flow rate
Pipe ID
Length
Roughness
Fluid properties

Expected outputs

Reynolds number
Friction factor
Pressure drop
Head loss

Formula overview

SI units: ΔP in Pa (or bar/kPa in the app), L and D in m, ρ in kg/m³, v in m/s.

ΔP = f · (L/D) · (ρ v² / 2), with the friction factor f from the Colebrook/Moody relationship.

Worked example

Example (turbulent): D = 0.1 m, L = 50 m, v = 2 m/s, ρ = 1000 kg/m³, f ≈ 0.02
ΔP = f × (L/D) × (ρv²/2)
ΔP = 0.02 × (50/0.1) × (1000 × 2² / 2) = 0.02 × 500 × 2000 = 20,000 Pa ≈ 0.2 bar.

Common mistakes

Forgetting to include minor losses from fittings, valves, and bends.
Using a constant friction factor without checking if the Reynolds number indicates laminar or turbulent flow.
Using nominal diameter instead of the actual inside diameter.