Compute frictional pressure drop in any straight pipe run using the Darcy-Weisbach equation with iterative Colebrook-White friction factor. Three fluid presets cover cold water, hot water, HVAC air, and saturated steam — with built-in roughness library for copper, plastic, commercial steel, cast iron, asphalt iron and galvanized iron pipes.
Pipe friction pressure drop drives pump head calculations, duct fan sizing, and steam main pressure budgets. The Darcy-Weisbach equation is the universal method, but its friction factor requires iterative solution of the Colebrook-White equation in turbulent flow. This tool automates the iteration and adds curated material roughness and fluid property presets so engineers can size any pipe run in seconds.
Universal method valid for any Newtonian fluid — water, air, steam, oils and process fluids.
Friction factor solved by Newton iteration on the implicit Colebrook-White formula — Moody-diagram accurate without manual lookup.
Water 20°C, water 80°C, air 20°C/1 atm, and saturated steam with built-in IAPWS density table — switch fluid without re-entering ρ and ν.
10 common materials with roughness values — copper, plastic, glass, new/old cast iron, new/old steel, asphalt iron, galvanized iron, concrete.
Results in Pa, kPa, bar, meters of head (mH2O) and specific resistance R in Pa/m — all units shown simultaneously.
Reynolds number, laminar/turbulent classification, and the friction factor method used — all returned for engineering auditability.
Choose water (20°C/80°C), air, or saturated steam. Density and viscosity auto-fill; steam also needs operating pressure.
Select pipe material from the library — roughness epsilon auto-fills. Or enter a custom value if you have manufacturer data.
Internal pipe diameter (mm), pipe length (m), and flow rate. Mass flow (kg/h) auto-converts to volumetric using density.
Get pressure drop, specific resistance, head loss, and flow regime in one call — all in multiple engineering units.
The Darcy-Weisbach equation is the universal method for frictional pressure drop in a straight pipe. It is valid for any Newtonian fluid and any flow regime — the only challenge is determining the friction factor λ (or f).
Reynolds number Re = ρ·v·D/μ = v·D/ν classifies the flow regime. Pipe flow is universally classified into three zones:
In turbulent flow, the friction factor satisfies the implicit Colebrook-White equation. This calculator solves it by Newton iteration with the Haaland explicit formula as initial guess — converges in fewer than 10 iterations to 1e-7 precision.
Saturated steam density varies strongly with pressure — from 0.598 kg/m³ at atmospheric pressure to 3.04 kg/m³ at 2 MPa gauge. This calculator embeds a 21-row IAPWS-IF97 saturation table and linearly interpolates density ρ and latent heat r from the user-entered gauge pressure.
| Water 20°C | Water 80°C | Air 20°C/1 atm | Saturated Steam | |
|---|---|---|---|---|
| Density ρ (kg/m³) | 998.2 | 972.0 | 1.204 | 0.6–3.0 (lookup) |
| Kinematic ν (m²/s) | 1.004×10⁻⁶ | 3.65×10⁻⁷ | 1.516×10⁻⁵ | ~2×10⁻⁷ (approx) |
| Flow unit | m³/h (volumetric) | m³/h | kg/h (mass) | kg/h (mass) |
| Typical application | Cold water supply | Heating hot water | HVAC ducts | Steam distribution mains |
| Extra input | None | None | None | Pressure (MPa g) |
Switch fluid, pick material, enter pipe size — get pressure drop in Pa/kPa/bar/mH2O instantly.