Friction Factor Calculator
This friction factor calculator estimates the value of friction factor for pipe flows which is used in several design calculations to determine the energy loss due to friction in pipe flows. The friction factor is commonly used in the DarcyWeisbach equation and is also referred to as the Darcy friction factor. This value depends on parameters like hydraulic radius, fluid viscosity, surface roughness, and Reynold's number. Read on to understand how to calculate friction factor using the Colebrook equation.
What are pipe losses and how to calculate friction factor?
The loss in energy of fluids while travelling through a pipe or ducts causes reduction in pressure and velocity which is known as head loss. The major causes of these losses include surface roughness and friction. In addition to this, changes in pipe crosssection like enlargement or contraction, bends, and branching contributes to minor losses. The friction head loss is used in the DarcyWeisbach equation to estimate the pressure drop Δp
for a fluid flowing at a velocity V
, in a pipe having length L
and diameter D
, and friction factor f
, such that:
Δp = f * L * V^{2} / (2 * g * D)
,where g
is the acceleration due to gravity.
The term f
, or friction factor, can be estimated for a pipe having surface roughness k
using the Colebrook equation:
1/√f = 2 * log(k / (3.7 * D) + 2.51/(Re * √f))
,where Re
is the Reynold's number for the fluid flow. The ColebrookWhite equation can only be solved using numerical approximations. One of the commonly used approximation is given by Lewis Moody, otherwise known as Moody chart or Moody diagram. This calculator utilizes Moody's approximation to determine the Darcy friction factor. Moody's approximation or otherwise known as Moody equation is given as:
f = 0.0055 ( 1 + (2 * 10^{4} * k/D + 10^{6}/Re)^{1/3})
This approximation is valid for flow regimes where Reynold's number is between 4,000
and 5*10^{8}
, and pipes with a k/D
ratio less than 0.01. This approximation is also used for this Moody diagram calculator.
How to calculate friction factor?
Follow the steps below to use the Moody equation to estimate the Darcy friction factor.

Step 1: Enter the hydraulic diameter of the pipe or conduit.

Step 2: Input the surface roughness of the pipe. Note that the equation is only valid for k/D ratio less than 0.01.

Step 3: Insert the Reynold's number for the flow regime. Note that the equation is only valid for pipe flows having Reynold's number in the range
4000
< Re <5*10^{8}
. 
Step 3A: You can use the
advanced mode
of calculator to estimate the Reynold's number. Use the fluid properties – density, viscosity, and flow velocity to find the Reynold's number. You can also use advanced mode to enter a value for the relative roughnessk/D
directly. 
Step 4: The Moody diagram calculator will return the value of Darcy friction factor.
Example: Using the Moody chart calculator
Find the friction factor for a pipe having a hydraulic diameter of 2 m
, a surface roughness of 0.01 m
. Take Reynold's number as 4500
.

Step 1: Enter the hydraulic diameter of the pipe or conduit,
D = 2 m
. 
Step 2: Input the surface roughness of the pipe,
k = 0.01 m
. Here,k/D
ratio is0.005
and therefore, acceptable. 
Step 3: Insert the Reynold's number for the flow regime,
Re = 4500
.f = 0.0055 * ( 1 + (2 * 10^{4} * k/D + 10^{6}/Re)^{1/3}) = 0.0055 ( 1 + (2 * 10^{4} * 0.01/2 + 10^{6}/4500)^{1/3}) = 0.04321

Step 4: The Moody chart calculator will return the value of Darcy friction factor,
f = 0.04321
.
FAQ
What are the factors affecting friction?
There are three main factors affecting friction – pipe diameter, Reynold’s number, and surface roughness. Reynold’s number for the flow depends on the flow velocity, fluid density and viscosity, and pipe length.
How to calculate friction factor for turbulent flow?
 Calculate the Reynold’s number for the flow (using ρ × V × D / μ).
 Check the relative roughness (k/D) to be under 0.01.
 Use the Reynold’s number, roughness in the Moody formula 
f = 0.0055 × ( 1 + (2×10^{4} × k/D + 10^{6}/Re)^{1/3})
How to use a moody friction factor chart?
To use a Moody friction factor chart, you need values for the Reynold’s number a relative roughness (k/D). Trace the relative roughness curve and draw a line from Reynold’s number on the xaxis. The point where the Reynold’s number line intersects the roughness curve gives the Moody friction factor.
How to calculate relative roughness of a surface?
You can calculate relative roughness of a surface using the formula: k/D, where k is the surface roughness and D is hydraulic diameter.