How to Calculate Torque

by Andy on January 28, 2013

64-094 Click Type Adjustable Torque Wrench with Ratcheting HeadWhen looking for torque tools, you may notice that a big consideration is the torque range. Torque range is important, as it shows the minimum and maximum power that the tool can put out. Most of the time, selecting the torque is as simple as matching a number on your product and your torque driver, but you may wonder where that number comes from. Also, the units for torque seem rather odd by most standards, as they combine a length (typically feet, inch, or meter) with force (pounds or newtons). Luckily, the answer to how to calculate torque can also help you understand why torque uses foot pounds or newton meters as their units!

Torque is force on an object that is created by twisting or turning it, so it is easiest to think of as a wrench turning a bolt. To calculate torque you take the amount of pressure and multiply it by how far away from the application point. For the purposes of our calculation, the amount of pressure is how hard you push the wrench and the distance from the application point is how far your hand is from the bolt.

If you applied 10lbs of force at 1 foot away then you would get:

10lbs X 1ft = 10ft.lbs

Now, you can see that your overall torque will change if you apply the pressure closer to or further away from the screw:

10lbs x 0.5ft = 5ft.lbs

10lbs x 2ft = 20ft.lbs

The further the force is from the point of application, the stronger the torque becomes. Alternately, you can say that it takes less pressure further away from the point of application to apply the same overall torque.

This is why we use wrenches to turn bolts, as it allows you to use much less pressure to turn a screw than just using your hand. If you needed 1ft.lbs to turn a screw, and your point of application was 1 inch away then it would take you 12lbs of pressure, as opposed to the 1lb of pressure from 1 foot away.

Also, this shows why you use units like ft.lbs, as you are saying how many pounds of pressure you need to use to turn the object at a point 1 foot away from the point of application. If you are dealing with smaller units of torque then you may use in.lbs. (inch pounds) or in.ozs (inch ounces), and when using the metric system you typically use Nm (newton meters) or Ncm (newton centimeters).

Do you have any other questions on torque? Leave a comment below! Thank you for reading, and be sure to check out our site at www.All-Spec.com for more information on specific products.

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