Pipe Friction Loss Calculator – Head Loss in Pipe Flow
Calculate pressure or head loss due to friction in pipes. Our pipe friction loss calculator uses the Darcy-Weisbach equation for accurate results in water and fluid systems.
Water at 20°C: 1×10⁻⁶ m²/s
Enter flow rate and pipe diameter
Input the volumetric flow rate in m³/s and the internal pipe diameter in meters.
Enter pipe length and roughness
Input the total pipe length in meters and the surface roughness in millimeters.
Set viscosity and calculate
Enter kinematic viscosity (1×10⁻⁶ m²/s for water at 20°C). Click Calculate to see head loss and pressure drop.
| Pipe Material | Roughness ε (mm) | Roughness ε (ft) |
|---|---|---|
| Drawn tubing (glass, brass) | 0.0015 | 0.000005 |
| Commercial steel pipe | 0.045 | 0.00015 |
| Galvanized iron | 0.15 | 0.0005 |
| Cast iron | 0.26 | 0.00085 |
| Concrete | 0.3 - 3.0 | 0.001 - 0.01 |
| Riveted steel | 0.9 - 9.0 | 0.003 - 0.03 |
What Causes Friction Loss?
As fluid flows through a pipe, it experiences resistance from the pipe walls. This resistance converts some of the fluid's energy into heat, causing a pressure drop along the pipe length. The amount of loss depends on flow velocity, pipe roughness, fluid viscosity, and pipe dimensions.
The Darcy-Weisbach Equation
Head loss is calculated using: hf = (f × L × v²) / (2 × g × D), where f is the friction factor, L is pipe length, v is velocity, g is gravity, and D is diameter. The friction factor depends on Reynolds number and relative roughness.
Friction Factor Calculation
For turbulent flow, this calculator uses the Swamee-Jain approximation: f = 0.25 / [log₁₀(ε/(3.7D) + 5.74/Re⁰.⁹)]². This provides accurate results without iterative calculation. For laminar flow (Re < 2000), f = 64/Re.
Flow Velocity
Head loss increases with the square of velocity. Doubling flow rate quadruples friction loss. This is the most significant factor in most systems.
Pipe Diameter
Larger diameter dramatically reduces loss. For the same flow rate, doubling diameter reduces velocity by 4x and head loss by about 30x.
Pipe Length
Head loss is directly proportional to length. A 200m pipe has twice the friction loss of a 100m pipe with identical conditions.
Pipe Roughness
Rougher pipes create more turbulence and higher friction. Effect is more pronounced at higher Reynolds numbers.
What's the difference between head loss and pressure drop?
Head loss is expressed in meters (or feet) of fluid column. Pressure drop is in Pascals (or psi). They're related by: ΔP = ρghf, where ρ is density, g is gravity, and hf is head loss.
Does this calculator include fittings and valves?
No, this calculates straight pipe friction only. Fittings, valves, and bends add additional losses. Use equivalent length method or K-factor method to account for fittings separately.
How accurate is the Swamee-Jain equation?
The Swamee-Jain approximation is accurate to within 1% of the Colebrook equation for typical pipe flow conditions. It's widely used in engineering because it doesn't require iteration.
Why is my pressure drop so high?
Common causes: pipe too small for flow rate, excessive flow velocity, very long pipe runs, or rough pipe material. Consider increasing pipe diameter or reducing flow rate.
What viscosity should I use for water?
At 20°C (68°F), water's kinematic viscosity is 1.004×10⁻⁶ m²/s. At 40°C it's 0.658×10⁻⁶ m²/s. Warmer water has lower viscosity and slightly lower friction loss.
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