Free engineering tool

Bolt Size Estimator (from load)

Arrive with a load, not a size: the smallest metric bolt and property class whose proof load carries your working load.

How this is calculated

Required force = working load × safety factor. Proof load of each size = tensile stress area × proof strength (ISO 898-1) for the chosen class. We recommend the smallest size whose proof load meets the required force. Reference estimate; verify critical joints against the drawing.

Axial working load (kN)Safety factorProperty class

Required force

20 kN

Recommended size

Proof load (this size)

21.2 kN

Headroom over required

+6%

Reference estimate — not a joint design

•Proof load is the safe working limit; keep the working load below it with the safety factor.
•A higher property class carries the same load in a smaller bolt — but needs the right material + heat treatment.
•Shear, fatigue, prevailing torque and embedment are not covered here — confirm critical joints against the drawing.

Bolt torque & proof load Steel grade hardening selector Request a quote

V.S. Heat Treatment

Heat treatment & metal finishing experts

Heating up

Bolt Size Estimator (from load)

How this is calculated

Reference estimate — not a joint design

Need a metal-plating expert?

Bolt Size Estimator (from load)

How this is calculated

Reference estimate — not a joint design