Bolt Torque Calculator
Calculate required bolt tightening torque to achieve a desired clamping force using the T = K×D×F short-form torque equation.
Inputs
psi
lb
Results
Required Torque
375 in·lb
Required Torque
31.3 ft·lb
Preload Force5,000 lb
Bolt Stress35,236 psi
% of Proof Load41.5%
Tensile Stress Area0.14 in²
How to Use This Calculator
- Select the Bolt Diameter from the dropdown — standard UNC sizes from 1/4" to 1-1/2".
- Enter the Proof Load Stress in psi: SAE Grade 5 ≈ 85,000 psi, Grade 8 ≈ 120,000 psi.
- Set the Nut Factor (K): use 0.20 for dry steel, 0.15 for lubricated threads, 0.12 for anti-seize.
- Enter your Desired Clamping Force in lb — typically 75% of the bolt proof load for static joints.
- Read the Required Torque in in·lb and ft·lb, and apply it with a calibrated torque wrench.
- Check the % of Proof Load to confirm you are not over-stressing the bolt (keep below 85–90%).
Ad Placeholder
Related Calculators
Weld Strength Calculator
Calculate weld strength for fillet and groove welds per AISC. Determine effective area, allowable load, and shear capacity with directional effects.
Pressure Vessel Design Calculator
Design cylindrical pressure vessels per ASME Section VIII. Calculate minimum wall thickness, hoop stress, and longitudinal stress.
Keyway Design Calculator
Design shaft keyways by calculating shear and compressive stresses in the key. Determine minimum key length and safety factor.
Ad Placeholder