Enter the tightening factor, axial force, and bolt diameter into the calculator to determine the flange bolt torque.

Flange Bolt Torque Formula

The following formula is used to calculate a flange bolt torque: 

T = k * f * d / 12
  • Where T is the flange bolt torque (ft-lb)
  • k is the tightening factor
  • f is the axial force (lbs)
  • d is the diameter of the bolt (inches).

To calculate the flange bolt torque, multiply the tightening factor by the axial force and the diameter, then divide by 12.

What is a flange bolt torque?

The flange bolt torque is the total torque that a flange bolt is subjected to when being tightened by a wrench.

The total torque required to tighten the bolt is dependent on the axial force seen by the bolt, the diameter, the tightening factor.

A tightening factor is a ratio or factor of safety that the bolt needs to be tightened to in order to sustain the axial load forces on the bolt.

How to claculate flange bolt torque?

The following example shows the steps and information needed to calculate a flange bolt torque.

First, determine the diameter of the bolt. In this example, the bolt has a diameter of 3 inches.

Next, determine the axial force seen by the bolt. In this example problem, the axial force on the bolt is measured to be 500 lbs-f.

Next, determine the tightening/nut factor. For this problem, the nut factor is 2.5.

Finally, calculate the flange bolt torque using the formula above:

T = k * f * d / 12

T = 2.5 * 500* 3 / 12

T = 312.5 ft-lbs