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 Darcy-Weisbach equation and is also referred to as the Darcy friction factor. This value depends on parameters like hydraulic radius, fluid viscosity, surface roughness, and Reynolds number. Read on to understand how to calculate friction factor using the Colebrook equation.

The loss in energy of fluids while traveling 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 cross-section like enlargement or contraction, bends, and branching contributes to minor losses. The friction head loss is used in the Darcy-Weisbach equation to estimate the pressure drop $\Delta p$ for a fluid flowing at a velocity $V$, in a pipe having length $L$ and the hydraulic diameter $D$, and friction factor $f$, such that:

where $g$ is the acceleration due to gravity.

You can read more about the pressure drop calculation with our dedicated Darcy-Weisbech calculator.

The term $f$, or friction factor, can be estimated for a pipe having surface roughness $k$ using the Colebrook equation:

where $\text{Re}$ is the Reynolds number for the fluid flow. The Colebrook-White 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:

This approximation is valid for flow regimes where Reynolds number is between $4,|!000$ and $5\cdot10^8$, and pipes with a $k/D$ ratio less than $0.01$. This approximation is also used for this Moody diagram calculator.

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 Reynolds number for the flow regime. Note that the equation is only valid for pipe flows having Reynolds number in the range $4000 < \text{Re} < 5\cdot10^8$.

• Step 3A: You can enter the Additional parameters into the calculator to estimate Reynolds number. Use the fluid properties – density, viscosity, and flow velocity to find Reynolds number. You can also use the Additional parameters field to enter a value for the relative roughness $k/D$ directly.

• Step 4: The Moody diagram calculator will return the value of the Darcy friction factor.

Find the friction factor for a pipe having a hydraulic diameter of $2 \text m$, a surface roughness of $0.01 \text m$. Take Reynolds number as $4500$.

• Step 1: Enter the hydraulic diameter of the pipe or conduit, $D = 2 \text m$.

• Step 2: Input the surface roughness of the pipe, $k = 0.01 \text m$. Here, $k/D$ ratio is $0.005$ and therefore, acceptable.

• Step 3: Insert the Reynolds number for the flow regime, $Re = 4500$.

• Step 4: The Moody chart calculator will return the value of Darcy friction factor, $f = 0.04321$.