How tight should a 1/2 inch bolt be?

Electrical & MechanicalASME B18.2.1 Fastener Torque

Bolt Torque & Clamping Force Calculator

Calculate tightening torque in foot-pounds (ft-lbs) and Newton-meters (N-m) for standard SAE and metric bolts to prevent gasket blowouts and thread stripping.

Electrical & Mechanical Field StandardsASME B18.2.1 Fastener Torque

Engineering formulations calibrated to IPC, UPC & NEC specificationsSub-Zero Cold Climate Tolerances

Quick Summary & Key Answer

Torque is calculated using the formula T = K × D × F, where K is the nut factor (0.20 dry, 0.15 lubricated), D is nominal bolt diameter in feet, and F is clamping force (typically 75% of proof strength). A standard 1/2"-13 Grade 5 bolt requires roughly 75 ft-lbs dry, but only 45-55 ft-lbs when lubricated with anti-seize.

Lubricating threads reduces friction, increasing clamping force by up to 50% at identical torque.
Grade 8 bolts have 6 radial hash marks on the hex head.
Flange bolts should be torqued in a criss-cross star pattern in 3 progressive passes.

Interactive Calculator

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Bolt Diameter & Thread Pitch

Fastener Grade / Material

Thread Lubrication Condition

Calculated OutputASME Torque Verified

Recommended Tightening Torque

84 ft-lbsft-lbs

Torque in Metric Newton-Meters: 115 N·m
Target Clamping Preload (F): 10,139 lbs
Torque in Inch-Pounds: 1,014 in-lbs

Note: Formula: T = K·D·F. Using anti-seize reduces required torque by roughly 40% compared to dry threads.

Flange Star Torquing Sequence

Torque flange bolts to 30%, then 60%, then 100% of final torque in a criss-cross pattern to ensure even gasket compression.

Frequently Asked Questions

Common questions regarding this calculation and code compliance

A 1/2-inch Grade 5 bolt should be torqued to approximately 75 ft-lbs dry, or 50 ft-lbs with anti-seize.