T = K × D × FThis free bolt torque calculator helps engineers, mechanics, and DIYers estimate the required tightening torque for metric and inch fasteners. Using the standard bolt torque equation T = K × D × F, we calculate preload based on bolt diameter, material strength class (ISO 8.8, 10.9, 12.9 / SAE Grade 5, 8), and friction factors for various lubrication conditions.
Whether you need a screw tightening torque calculator for automotive work, a bolt stress calculator for engineering analysis, or a general fastener torque calculator for industrial applications, this tool provides reliable estimates. It also works as a nut torque calculator for hex nuts and threaded fasteners.
The standard formula is T = K × D × F, where T is torque (N·m), K is the friction factor, D is bolt diameter (m), and F is clamping force (N). This equation is used in most bolt tightening torque calculations.
Our bolt stress calculator uses the tensile stress area (As) and yield strength to determine maximum preload. Select your bolt's strength class to see the stress area and resulting clamping force.
K = 0.20 is typical for dry, clean steel. Lubricated threads use K = 0.10–0.15. Anti-seize compounds can reduce K to 0.08–0.12. Always verify with manufacturer specifications for critical applications.
Yes. The torque values apply to both bolt heads and nuts. Use the same diameter and strength class for accurate nut torque calculations.