Fasteners

Bolt Torque Calculator

Calculate recommended tightening torque based on bolt size, grade, and lubrication.

Input Parameters

Units:

Bolt Size

Bolt Grade

Lubrication

Results

Select parameters and click Calculate

What is Bolt Torque?

Bolt torque is the rotational force applied to a fastener to create clamping force (preload) in a bolted joint. Proper torque ensures the joint can handle design loads without loosening or failing.

The relationship between applied torque and resulting clamping force depends on thread friction, bolt grade, and lubrication condition. This is why torque specifications vary significantly based on these factors.

How to Use

Select your unit system (Imperial or Metric)
Choose your bolt size from the dropdown
Select the bolt grade for your application
Specify the lubrication condition of the threads
Click Calculate to get the recommended torque

FAQs

Proper torque ensures the bolt develops the correct clamping force. Under-torquing can lead to joint loosening or failure, while over-torquing can strip threads, break fasteners, or damage mating surfaces.

Lubrication reduces friction in the threads, meaning more of your applied torque converts to clamping force. This is why lubricated bolts require lower torque values - the same torque on a lubricated bolt produces more clamping force.

Grade 5 bolts are medium carbon steel with a tensile strength of 120,000 psi. Grade 8 bolts are alloy steel with 150,000 psi tensile strength. Grade 8 is used for higher stress applications but is more brittle.

No. Anti-seize is mainly for preventing galling in stainless steel or where bolts may be exposed to corrosion. When using anti-seize, you must reduce torque by about 35% to avoid over-stressing the bolt.

No. Torque-to-yield (TTY) bolts are designed to stretch into the plastic deformation zone. Once stretched, they cannot return to their original state and must be replaced.

Limitations

• Values are recommendations based on standard engineering tables
• Does not account for joint stiffness or gasket factors
• Assumes standard thread engagement (1.5x diameter minimum)
• Not suitable for torque-to-yield (TTY) fasteners
• Always verify with manufacturer specs for critical applications