Pipe Sizing Calculator

Find the required pipe diameter for a given flow rate and allowable head loss using Darcy-Weisbach with iterative friction factor.

Pipe Networks · Design

Fluid Presets

Inputs

Volume flow rate Q (L/s)

Allowable head loss hf (m)

Pipe length L (m)

Absolute roughness ε (m)

Fluid density ρ (kg/m³)

Dynamic viscosity μ (Pa·s)

Q = 50 L/s = 0.050000 m³/s

Theory

Darcy-Weisbach Rearranged for Diameter

hf = f × (L/D) × V²/(2g) and V = Q/A = 4Q/(πD²)

→ D = (8fLQ² / (π²g hf))^(1/5)

Iterative Solution

Initial guess: D₀ from assumed velocity V₀ ≈ 1.5 m/s
Compute Re = ρVD/μ and ε/D
Update f (Swamee-Jain explicit)
Solve for new D = (8fLQ²/(π²g hf))^(1/5)
Repeat until |ΔD/D| < 10⁻⁸

Velocity Design Guidelines (water)

Application	V (m/s)
Minimum — sediment avoidance	0.3–0.6
Distribution mains	0.6–1.5
Pumped water supply	1.0–2.5
Short high-flow connections	2.0–3.0
Maximum — erosion / noise limit	< 3.0

The calculated D is the minimum hydraulic requirement. Always select the next larger standard nominal bore (DN). A larger pipe reduces velocity, head loss, and long-term pumping energy costs.