Bolt Tightening Torque & Preloadv1.0.0Method: Bolt Torque

Bolt Tightening Torque & Preload Calculator

Calculate tightening torque, clamp force preload, and thread stress per VDI 2230 and ASME PCC-1 across metric ISO and imperial bolt grades.

Bolt Size (Metric ISO coarse)

Target Utilization (Proof)

Bolt Strength Class / Grade

ISO 8.8 (High Tensile Medium Carbon) · proof strength Sp = 580 MPa (≤ M16)

Lubrication & Surface Condition

Bolted Joint Section

VDI 2230 short-form · T = K · d · Fp

Ready to calculate

Enter values and press Calculate to see results.

VDI 2230 Part 1Governing Code

Systematic calculation of high duty bolted joints — Joints with one cylindrical bolt

Scope:Preload, thread and underhead friction, and clamp load calculation.

ASME PCC-1Governing Code

Guidelines for Pressure Boundary Bolted Flange Joint Assembly

Scope:Bolt target preloads, torque calculations, and assembly patterns.

ISO 898-1Governing Code

Mechanical properties of fasteners made of carbon steel and alloy steel

Scope:Proof loads, tensile strengths, and yield points for property classes.

Literature & Further Reading

[1]VDI 2230 — Systematic Calculation of Bolted Joints.
[2]ASME PCC-1 — Guidelines for Pressure Boundary Bolted Flange Joint Assembly.
[3]Bickford, J.H. — An Introduction to the Design and Behavior of Bolted Joints.

Practical checks before using the result

Short-form torque

T = K · d · Fp

Nut-factor method (VDI 2230 simplified form)

Target preload

Fp = η_util · As · Sp

Proof-strength basis per ISO 898-1 / SAE J429

Torque only indirectly sets preload: most of the wrench torque is lost to friction, so the nut factor K dominates the result.

Use the K value for the actual lubricant and finish. Anti-seize (K ≈ 0.12) instead of dry threads (K ≈ 0.20) gives ≈ 65 % more preload at the same torque.
Use a calibrated torque wrench and a star / cross-pattern sequence in several passes on flanges.

Never lubricate threads without lowering the torque — the same torque can then yield or break the bolt.
Torque control scatters preload by roughly ±25 %; use tensioning or bolt elongation where preload is critical.

Does not check joint separation, slip, fatigue or embedding losses — use the full VDI 2230 procedure for those.
Does not size flange gasket stress or bolt-up for ASME PCC-1 / ASME VIII Appendix 2 flanges.