Enter the material constant, the nominal bolt diameter (ft), lubrication factor, and the axial bolt force (lbf) into the calculator to determine the Screw Torque.

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## Screw Torque Formula

The following formula is used to calculate the Screw Torque.

**Ts = K*F*d * (1-L / 100)**

- Where Ts is the Screw Torque (lb-ft)
- K is the material constant
- .2 for normal steel bolts from .250″ to 1″

- d is the nominal bolt diameter (ft)
- F is the axial bolt force (lbf)
- L is the force lost due to lubrication (%)

## How to Calculate Screw Torque?

The following example problems outline how to calculate Screw Torque.

**Example Problem #1**

- First, determine the material constant. In this example, the material constant is determined to be .2 .
- Next, determine the nominal bolt diameter (ft). For this problem, the nominal bolt diameter (ft) is measured to be .25.
- Next, determine the axial bolt force (lbf). In this case, the axial bolt force (lbf) is found to be 1000.
- Next, determine the loss due to lubrication. In this example, this is 50%.
- Finally, calculate the Screw Torque using the formula above:

Inserting the values from above and solving yields:

Ts = K*F*d * (1-L / 100)** = **(lb-ft)

Ts = .2*1000*.25 * (1-50 / 100) = 25 lb-ft

**Example Problem #2**

Using the same method as above, determine the variables required by the formula. For this example problem, these are:

material constant = .2

nominal bolt diameter (ft) = .3

axial bolt force (lbf) = 5000

lubrication loss (%) = 35

Enter these given values into the calculator or above yields:

Ts = .2*5000*.3 * (1-35 / 100) = 195** **(lb-ft)