Bolt Torque Calculator
Calculate optimal bolt tightening torque and clamping force using T = K×F×d×(1-l/100)
Calculate Bolt Torque and Clamping Force
Standard zinc-plated mild steel bolts
The nominal diameter of the bolt shaft (not the head)
No lubrication applied
The force needed to properly clamp the joined materials
Required Torque Results
Formula: T = K × F × d × (1 - l/100)
Where: K = 0.2, F = 0 N, d = 0.0 mm, l = 0%
Lubrication Reduction: 0% (0.0 N⋅m reduction)
⚠️ Critical Safety Warning
• Always consult manufacturer torque specifications when available
• Over-tightening can cause bolt failure, thread damage, or material cracking
• Under-tightening may result in joint failure or bolt loosening
• Use calibrated torque wrenches for critical applications
• This calculator provides estimates - verify with engineering standards
Example Calculation
Structural Steel Connection
Bolt: M12 zinc-plated mild steel bolt
Diameter: 12 mm (0.012 m)
Material: Mild steel, zinc-plated (K = 0.2)
Lubrication: SAE 30 motor oil (40% reduction)
Required Clamping Force: 15,000 N
Calculation Steps
T = K × F × d × (1 - l/100)
T = 0.2 × 15,000 N × 0.012 m × (1 - 40/100)
T = 0.2 × 15,000 × 0.012 × 0.6
T = 36 × 0.6
T = 21.6 N⋅m
Convert to lb⋅ft: 21.6 ÷ 1.356 = 15.9 lb⋅ft
Standard Bolt Torques
Metric Bolts (Steel)
Imperial Bolts (Steel)
⚠️ Values for standard grade bolts. Always verify with specifications.
K Constants by Material
Values for bolts 1/4" to 1" diameter
Lubrication Effects
Dry threads require higher torque
Oil reduces required torque by 15-40%
Anti-seize compounds provide 45% reduction
Over-lubrication can reduce clamping force
Understanding Bolt Torque
What is Bolt Torque?
Bolt torque is the rotational force applied to tighten a bolt, creating tension in the bolt that generates clamping force between joined materials. Proper torque ensures secure connections without damaging the bolt or materials.
Why is Proper Torque Critical?
- •Under-torquing leads to loose joints and potential failure
- •Over-torquing can cause bolt breakage or thread damage
- •Consistent torque ensures uniform clamping force
- •Proper torque maximizes joint reliability and safety
Torque Formula
T = K × F × d × (1 - l/100)
- T: Applied torque (N⋅m or lb⋅ft)
- K: Material and coating constant (0.15-0.35)
- F: Clamping force (N or lbf)
- d: Bolt diameter (m or ft)
- l: Lubrication factor (0-80%)
Important: This formula is an approximation. Always consult manufacturer specifications and engineering standards for critical applications.