Moody Friction Factor Calculator

Select Calculation:
Circular Duct: Enter D and Q	Kinematic viscosity, ν (L²/T):
Circular Duct: Enter D and V	Surface Roughness, e (L):
Circular Duct: Enter D and Re	Duct Diameter, D (L):
Non-circular Duct: Enter A, P, and Q	Duct Area, A (L²):
Non-circular Duct: Enter A, P, and V	Duct Perimeter, P (L):
Non-circular Duct: Enter A, P, and Re	Velocity, V (L/T):
LMNO Engineering,	Discharge, Q (L³/T):
Research, and Software, Ltd.	Reynolds Number:
www.LMNOeng.com	e/D:
	Moody Friction Factor, f:

Friction Factor Equations

D = Diameter of a circular duct. If duct is non-circular, then D is computed as the hydraulic diameter of a rectangular duct, where D = 4A / P per our non-circular duct page.
Re = Reynolds Number. The symbol Re is not the product (R)(e).

Kinematic viscosity (ν) depends on the fluid (water, air, etc.). Click for kinematic viscosity table.
Surface roughness depends on the duct material (steel, plastic, iron, etc.). Click for surface roughness table.

The equations used in this program represent the Moody diagram which is the old-fashioned way of finding f. You may enter numbers in any units, so long as you are consistent. (L) means that the variable has units of length (e.g. meters). (L³/T) means that the variable has units of cubic length per time (e.g. m³/s). The Moody friction factor (f) is used in the Darcy-Weisbach major loss equation. Note that for laminar flow, f is independent of e. However, you must still enter an e for the program to run even though e is not used to compute f. Equations can be found in Discussion and references for pipes, culverts.

A more complicated equation which represents a slightly larger range of Reynolds numbers and e/D's is used in Design of Circular Liquid or Gas Pipes.

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