— m/s
WATER SYSTEMS
Water pipe sizing
Select internal diameter for your flow rate and operating conditions.
Design inputs
Example starting values; adjust to project requirements. Pure water only, no glycol.
mm
m/s
Pa/m
°C
mm
m
%
%
m/s
m/s
Use actual internal diameter, not DN or outside diameter. The 15–1,000 mm list is illustrative; verify wall thickness and pipe class with the manufacturer.
RECOMMENDED DIAMETER
—
Full pipe area—Reynolds—Friction factor—
— Pa/m
— kPa
Understanding the results
Method & scope ＋
Pressurized pipes: V = Q/A; Re = ρVD/μ; R = fρV²/(2D). Darcy factor uses 64/Re for laminar flow and Colebrook for Re ≥ 4,000. The 2,300–4,000 transition region is interpolated and flagged. Density and viscosity are approximated for pure water at 1–80 °C.
Gravity drainage: Q = A·Rh^(2/3)·√S/n, with Rh = A/P. Normal flow depth in a circular pipe is solved from flow, slope and Manning n. Maximum depth is limited to 10–80% to use the monotonic branch. Only pipes with sufficient capacity and velocities within the minimum and maximum limits are retained.
Straight pipe sections only; excludes fittings, valves, equipment, elevation changes, required residual pressure, unsteady flow and branched networks. Material and design presets are editable reference values.
EPA EPANET — pressurized pipes · EPA SWMM — drainage hydraulics