Engineering · Calculators

Bolt torque calculator.

Recommended assembly torque for inch and metric bolts at 75% of yield preload. Adjusts for fastener grade and lubrication. For critical assemblies, always cross-check with the manufacturer's torque chart.

Torque — ft-lb · — N·m details ↓

Bolt size Bolt grade / strength

Preload as % of yield %

Standard structural assembly = 75% of yield. Reduce to 50–60% for soft mating materials, raise to 85–90% for fatigue-resistant joints with hardened washers.

Recommended torque

Imperial

— ft-lb

— in-lb

Metric

— N·m

Tensile area:—

Yield strength:—

Preload force:—

Nut factor (K):—

Send these numbers to a quote →

For aerospace/critical joints, cross-check with the OEM specification. For tapped holes in soft material (aluminum, plastics), reduce torque to limit thread engagement strain.

Yield Limit Safety Meter

75%

of yield strength

Torque Energy Distribution

11%

49%

40%

Preload (11%) Under-head (49%) Thread (40%)

Physics Note: Around 90% of applied torque is consumed by under-head and thread friction — roughly half under the head/nut face, ~40% in the threads (NASA RP-1228; Bickford). Only the remainder converts to clamp force.

Joint Simulator

Fastener Preload & Plate Compression

PASS (Safe)

Elongation / Stretch

0.0000″ elastic stretch

Elastic Stress

0.0 ksi of 92.0 ksi yield

Calculation method: T = K × D × F, where T is torque, K is the nut factor (varies by lubrication, default 0.20 dry steel), D is nominal bolt diameter, and F is the target preload force (75% × yield × tensile stress area).

Keep exploring

Related tools & references

Thread engagement calculator→

Engagement length so the joint fails the bolt, not the threads.

Thread specs reference→

Tensile stress areas and pitch behind these torque values.

Tap drill calculator→

Pick the right tap drill for the mating tapped hole.

Clearance hole chart→

Through-hole sizes for bolted joints.

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