liminfoPipe Pressure Drop Calculator
Free web tool: Pipe Pressure Drop Calculator
Steel: 0.045mm, PVC: 0.0015mm, Cast iron: 0.26mm
Fittings
Breakdown
About Pipe Pressure Drop Calculator
The Pipe Pressure Drop Calculator computes fluid pressure drop and total head loss in a straight pipe system including fittings, using the Darcy-Weisbach equation combined with the Colebrook-White iterative method for the Darcy friction factor. You input pipe diameter (mm), pipe length (m), volumetric flow rate (m³/h), pipe roughness (mm), and select the fluid type from a library of common fluids. You can add multiple pipe fittings from a library of 14 fitting types — including elbows, tees, valves, and entrance/exit losses — each with a standard K-factor. The tool calculates flow velocity, Reynolds number, flow regime (laminar or turbulent), friction factor, pipe friction head loss, fittings head loss, total head loss, and total pressure drop in kPa.
This calculator is used by mechanical engineers, piping designers, HVAC engineers, plumbers, and process engineers who need to size pumps, select pipe diameters, verify flow rates, or calculate the total head a pump must deliver in a system. Accurate pressure drop calculations are critical for pump selection, energy efficiency analysis, and ensuring that flow rates are achievable with available pressure. The Colebrook-White equation is solved iteratively (50 iterations) to converge on the Darcy friction factor for turbulent flow, and the Hagen-Poiseuille formula (f = 64/Re) is used directly for laminar flow (Re < 2300).
All supported fluids include density and dynamic viscosity data at typical operating conditions: Water at 20°C (998 kg/m³, 0.001 Pa·s), Water at 60°C (983 kg/m³, 0.000467 Pa·s), Light Oil (850 kg/m³, 0.01 Pa·s), Heavy Oil (920 kg/m³, 0.1 Pa·s), and Air at 20°C and 1 atm (1.204 kg/m³, 0.0000181 Pa·s). Pipe roughness guidance is provided for steel (0.045 mm), PVC (0.0015 mm), and cast iron (0.26 mm). All computation happens in your browser with no server calls.
Key Features
- Uses the Darcy-Weisbach equation for pipe friction head loss with Colebrook-White friction factor
- Iterative Colebrook-White solution (50 iterations) for accurate turbulent friction factor
- Hagen-Poiseuille formula for laminar flow (Re < 2300) with automatic regime detection
- Supports 5 built-in fluids with density and viscosity: water (20°C/60°C), light oil, heavy oil, and air
- Pipe fittings K-factor library with 14 fitting types including elbows, tees, valves, and entrance/exit
- Add or remove multiple fittings and adjust counts interactively
- Shows velocity, Reynolds number, friction factor, pipe loss, fittings loss, and total head and pressure drop
- Provides roughness reference values for steel, PVC, and cast iron pipe
Frequently Asked Questions
What equation does this calculator use for pressure drop?
The calculator uses the Darcy-Weisbach equation: hf = f × (L/D) × (V²/2g), where hf is head loss in meters, f is the Darcy friction factor, L is pipe length, D is pipe diameter, V is flow velocity, and g is gravitational acceleration. The friction factor is computed using the Colebrook-White equation for turbulent flow, or f = 64/Re for laminar flow.
What is the Colebrook-White equation?
The Colebrook-White equation is an implicit formula for the Darcy friction factor in turbulent pipe flow: 1/√f = -2 log₁₀(ε/(3.7D) + 2.51/(Re√f)), where ε is pipe roughness and Re is Reynolds number. Because it is implicit in f, it is solved iteratively. This calculator runs 50 iterations starting from f = 0.02, which is more than sufficient for convergence to engineering accuracy.
What is the Reynolds number and what does it indicate?
The Reynolds number (Re = ρVD/μ) is a dimensionless ratio of inertial to viscous forces. Re < 2300 indicates laminar flow (smooth, layered flow); Re > 4000 indicates fully turbulent flow; 2300–4000 is the transitional region. This calculator uses Re = 2300 as the laminar/turbulent cutoff for selecting the appropriate friction factor formula.
How are fitting losses calculated?
Fitting losses are calculated using the K-factor method: hf = K × V²/(2g), where K is a dimensionless resistance coefficient for each fitting type. The total K of all fittings is summed, and the combined head loss is added to the straight-pipe friction loss to get the total head loss. K values are standard industry values for common fitting types.
What pipe roughness values should I use?
Pipe roughness (absolute roughness, ε) depends on pipe material. Common values: drawn tubing and PVC — 0.0015 mm; commercial steel and wrought iron — 0.046 mm; cast iron — 0.26 mm; galvanized iron — 0.15 mm; concrete — 0.3–3 mm; riveted steel — 0.9–9 mm. The calculator provides reference values for steel, PVC, and cast iron.
How do I convert head loss (m) to pressure drop (kPa)?
Pressure drop = head loss × fluid density × gravitational acceleration / 1000. In this calculator, the conversion is: ΔP (kPa) = hf (m) × ρ (kg/m³) × 9.81 (m/s²) / 1000. For water at 20°C (998 kg/m³), 1 m of head corresponds to approximately 9.79 kPa. For less dense fluids like air, the pressure equivalent of a given head is much smaller.
What is the difference between laminar and turbulent flow in piping?
In laminar flow (Re < 2300), fluid moves in parallel layers with no cross-flow mixing. The friction factor depends only on Reynolds number (f = 64/Re) and is independent of pipe roughness. In turbulent flow (Re > 4000), fluid mixes chaotically and friction depends on both Re and pipe roughness, requiring the Colebrook-White equation. Turbulent flow is the norm in most engineering piping systems.
Can this calculator be used for gas or air systems?
Yes — Air at 20°C (1 atm) is one of the built-in fluid options with density 1.204 kg/m³ and dynamic viscosity 0.0000181 Pa·s. The Darcy-Weisbach equation applies equally to liquids and gases for incompressible flow conditions. For high-pressure or high-velocity gas systems where compressibility effects are significant, a more specialized compressible flow analysis would be needed.