Moody Chart Calculator

What this calculator does

Finds Darcy friction factor from Reynolds number and relative roughness, then plots the operating point on a generated Moody diagram.

Inputs

Reynolds number

Relative roughness ε/D

For a 100 mm pipe with 0.045 mm roughness, ε/D = 0.00045.

Reynolds number must be positive and relative roughness must lie between 0 and 0.1.

The transitional range has no single reliable friction-factor curve.

Results

Darcy friction factor

—

Flow regime

—

Fanning factor

—

Fully rough limit

—

Reading: —

Moody diagram

Solid curves: constant ε/DOrange point: current inputShaded bands: laminar / transition / turbulent regions

The chart is generated locally; both axes are logarithmic, matching the standard Moody diagram convention.

What the Moody diagram shows

The Moody diagram relates Darcy friction factor to Reynolds number and relative roughness ε/D for fully developed flow in circular pipes.

Why friction factor matters

Darcy friction factor is the multiplier in hL = f(L/D)V²/(2g). A small change in f acts directly on calculated straight-pipe head loss and pressure drop.

How to use the chart

Find Reynolds number on the horizontal logarithmic axis, move to the curve for the pipe’s relative roughness, then read Darcy friction factor on the vertical logarithmic axis. The orange point performs this reading numerically.

Flow regions

Laminar flow follows f = 64/Re and is independent of roughness. The transition band has no unique reliable curve. In turbulent flow, both Reynolds number and roughness matter; at very high Re the fully rough limit becomes nearly independent of Re.

Darcy versus Fanning factor

The chart and main result use Darcy friction factor. The Fanning factor is one quarter of the Darcy value. Mixing the two conventions produces a fourfold pressure-loss error.