Bolt Torque Calculator

Created by Kenneth Alambra
Last updated: Jul 09, 2022

This bolt torque calculator will help you know how much bolt torque to apply to your threaded fasteners to achieve a specified clamping force when fastening two or more materials together. Conversely, you can also use this tool as a bolt clamping force calculator to find the resulting clamping force of any applied bolt torque.

In this calculator, you will also learn:

  • What bolt torque is;
  • The bolt tightening torque formula we used in this tool;
  • How to calculate bolt torque; and
  • How to use this bolt torque calculator.

Ready to learn? Then keep on reading.

What is bolt torque?

Bolt torque is basically the torque one should apply to a bolt to achieve a particular clamping force. Factors affecting the bolt torque are the bolt material and diameter and the lubrication applied to the bolt threads.

Tightening a bolt and nut together also applies a clamping force on the object between them. That means we translate the rotational force on our threaded fastener (in this case, the nut and bolt) to a linear clamping force. The tighter we fasten them, the higher the clamping force is. However, we would want to apply the ideal amount of torque to our threaded fasteners to prevent our assembly of parts from falling apart.

Applying too much bolt torque could result in the shearing of our fastener's threads or the elongation of the bolt's shaft. Not enough bolt torque could lead to loosening of the fasteners. Both of these events could result in the failure to achieve the required clamping force.

That's why it is great to learn how to calculate bolt torque values for bolts. In the next section of this text, let's learn the bolt tightening torque formula so we can start performing bolt torque calculations.

How to calculate bolt torque using the tightening torque formula

The bolt tightening torque calculation formula that we use in this calculator is as follows:

T=K×F×d×(1l100)T = K\times F\times d\times (1 - \frac{l}{100})

where:

  • TT is the torque we need to apply to tighten the bolt;
  • KK is the constant factor that represents the bolt material and finish;
  • FF is the clamping force the bolt applies to the fastened objects;
  • dd is the bolt diameter; and
  • ll is the lubrication factor percentage.

How to use this bolt torque calculator

Here are the steps you can follow when using this bolt torque calculator:

  1. Select the bolt type of the threaded fastener you wish to use. Doing so will designate a value for constant K for a range of 1/4" to 1" bolt diameters. You can also enter the value for the constant K if you know your bolt type's constant factor.
  2. Enter the diameter of your bolt's cylindrical shaft.
  3. Choose the lubrication you want to use, or you can input the lubrication factor percentage you plan to apply to your threaded fastener.
  4. Input the clamping force you need to achieve. After that, our tool will instantly display the estimated bolt torque to meet that clamping force.

You can also use our tool as a bolt clamping force calculator if you know your fastener's bolt torque. To do that, skip step 4 and enter the bolt torque to find the clamping force.

Kenneth Alambra
T = K·F·d(1 - l/100)
Bolt type
Mild-steel, dry
Constant K
Diameter (d)
in
Lubrication
Lubricant
No lubricant
Lubrication factor (l)
%
Force and torque
Clamping force (F)
lbf
Torque (T)
ft-lb
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