Bolt Torque Calculator

Calculate recommended torque values for bolts by size, grade, and lubrication.

Fastener System

Bolt Size

Grade / Class

Lubrication Condition

Target Preload (% of Proof Load)

Typically 70-80% for reusable joints

Recommended Torque

ft-lbs

Torque (Nm)

Torque (in-lbs)

Clamp Force

lbf

Proof Load

lbf

Tensile Strength

Bolt Torque Formula

T = K x D x F

T = Torque, K = Nut Factor, D = Nominal Bolt Diameter, F = Desired Clamp Force

Grade 2: Low carbon steel. 74,000 PSI tensile. General purpose.
Grade 5: Medium carbon, quenched/tempered. 120,000 PSI. Most common structural grade.
Grade 8: Alloy steel, Q&T. 150,000 PSI. High-strength applications.

Thread dimensions.

Drill bit sizes.

Rivet sizing.

Metal weight.

Steel section properties.

Fatigue life estimation.