Bolt Torque Specifications & Tightening Standards: Metric & Imperial Guide

The Standard Bolt Torque Formula

Tightening torque is calculated using the formula: T = K × D × F

• T: Tightening Torque (Nm or in-lbs).
• K: Torque coefficient (approx. 0.20 for dry zinc-plated steel; 0.15 for lightly oiled fasteners; 0.10 for anti-seize paste).
• D: Nominal bolt diameter (meters or inches).
• F: Target bolt clamping preload (typically 75% of proof load).

Metric Grade 8.8 & 10.9 Standard Tightening Torque (Nm, Dry Condition)

Bolt Size	Grade 8.8 (Nm)	Grade 10.9 (Nm)	Grade 12.9 (Nm)
M6	9.5 Nm	14 Nm	16 Nm
M8	23 Nm	34 Nm	40 Nm
M10	46 Nm	68 Nm	79 Nm
M12	79 Nm	117 Nm	136 Nm
M16	195 Nm	285 Nm	335 Nm
M20	380 Nm	560 Nm	650 Nm