Calculate head loss and pressure drop in pipes using the Darcy-Weisbach equation. Compare pipe materials, sizes, and flow conditions for plumbing, HVAC, and hydraulic systems.
Friction loss describes the energy dissipated as heat when fluid flows through a pipe due to viscous shear between the fluid and the pipe wall. The Darcy-Weisbach equation — h_f = f(L/D)(v²/2g) — is the fundamental formula for calculating this head loss, applicable to any Newtonian fluid in any pipe geometry.
For engineers designing water distribution, HVAC, fire protection, or chemical process systems, friction loss directly determines pump sizing, pipe cost, and energy consumption. A pipe that is one size too small can double the friction loss, quadrupling pump power requirements due to the velocity-squared relationship.
This calculator computes head loss and pressure drop from pipe geometry and flow conditions, includes a clickable pipe material reference, generates pipe diameter comparison tables showing how upsizing reduces losses, and visualizes the relative friction loss across common materials — providing everything needed for practical pipe system design. Check the example with realistic values before reporting.
Friction loss calculations involve friction factor lookup (Moody chart or Colebrook equation), unit conversions, and cross-referencing pipe dimensions. This calculator combines all steps: it solves for friction factor, head loss, pressure drop (Pa, psi, bar), flow rate, and pump power in one click. Material and diameter comparison tables let you evaluate design alternatives instantly.
Darcy-Weisbach Equation: h_f = f × (L/D) × v²/(2g) Pressure Drop: ΔP = f × (L/D) × ρv²/2 Pump Power: P = ΔP × Q = ΔP × Av where: f = Darcy friction factor (from Colebrook-White or 64/Re for laminar) L = pipe length (m), D = pipe diameter (m) v = flow velocity (m/s), g = 9.81 m/s² ρ = fluid density (kg/m³), Q = volumetric flow rate (m³/s)
Result: h_f = 4.26 m, ΔP = 41.7 kPa
100 m of 4" commercial steel pipe (ε = 0.045 mm) with water at 2 m/s: Re = 202,390, f = 0.0218. Head loss = 0.0218 × (100/0.1016) × 4/(2 × 9.81) = 4.26 m. Pressure drop = 998 × 9.81 × 4.26 = 41.7 kPa (6.1 psi). Pump power = 41,700 × 0.0162 = 676 W to overcome friction.
The most important practical insight in pipe hydraulics is the fifth-power relationship between diameter and head loss at constant flow rate. If you need a specific flow rate Q, the velocity in a pipe of diameter D is v = Q/(πD²/4). Substituting into Darcy-Weisbach: h_f ∝ v² × L/D ∝ Q² × L/D⁵. This means doubling the diameter reduces friction loss by a factor of 32 — often justifying the higher cost of larger pipe.
Engineers typically size pipes by selecting a maximum acceptable velocity (1.5–2.5 m/s for water supply, 3–5 m/s for fire protection) or a maximum head loss per unit length (often 0.03–0.05 m per meter for distribution mains). This calculator\'s diameter comparison table directly supports this workflow: enter your required flow rate, then read which pipe sizes meet your head-loss budget.
For continuously operating systems (water treatment, industrial processes), friction loss translates directly to electricity cost. Power = ΔP × Q / η_pump. At $0.10/kWh, a pump overcoming 50 kPa at 10 L/s costs about $4,400/year. Reducing friction by 50% through pipe upsizing pays for itself quickly — a calculation this tool supports with its pump power output.
Head loss (h_f) is measured in meters of fluid column — it\'s independent of fluid density and represents energy loss per unit weight. Pressure drop (ΔP = ρgh_f) is in Pascals and depends on density. Engineers use head loss for pump curves and pressure drop for piping specifications.
No. The friction factor depends only on Reynolds number and relative roughness. However, head loss is directly proportional to length: doubling the pipe length doubles the friction loss.
Head loss scales as 1/D for the same velocity. But to maintain the same flow rate in a smaller pipe, velocity must increase (V ∝ 1/D²). Since h_f ∝ V²/D, the total effect is h_f ∝ 1/D⁵ for constant flow rate. Halving the diameter increases losses by 32×!
This calculator handles major (friction) losses only. Minor losses from elbows, tees, valves, and reducers are calculated separately using h_m = K × v²/(2g). In long straight pipes, major losses dominate; in compact systems with many fittings, minor losses can exceed friction losses.
Higher temperature lowers water viscosity, increasing Reynolds number and slightly changing friction factor. More importantly, lower viscosity means more turbulent flow. Overall, warmer water has slightly less friction loss than cold water at the same flow rate.
SI units throughout: meters, m/s, Pa, kg/m³. Results also show psi and bar for pressure. For imperial pipe sizes, use the diameter comparison table which lists nominal pipe sizes with their metric inner diameters.