How do you choose sheet thickness?

Choose thickness for the part’s role, dimensions and fixings. A cover hiding a mechanism and a load-bearing plate have different requirements, even if their overall shapes are similar.

A large flat face and a profile with flanges behave differently. Compare a thicker flat version with a bent version, allowing for bending costs and available space.

For a 600 × 400 mm cover, for example, prepare a flat plate and a flanged cover with identical fixings. Ask for an assessment of deflection and fabrication. This comparison alone does not establish an acceptable thickness.

At identical area and material, mass is proportional to thickness. A 1 m² steel plate weighs about 15.7 kg at 2 mm and 23.55 kg at 3 mm: increasing from 2 to 3 mm adds 50% mass.

This extra weight matters for handling, hinges, supports and transport. Finished prices need not rise by the same percentage, since they also include cutting, setup and other operations.

A part may remain elastic yet deflect too much for its purpose. Define both the load and acceptable deflection. Material name or thickness alone answers neither question.

Changing grade or replacing steel with aluminium requires a design review. Lower mass does not mean the same geometry will retain the same behaviour.

Thickness affects bend radius, minimum flange length and hole-to-bend distance. These also depend on material and tooling: confirm constraints before finalising the drawing.

Ask which thicknesses and grades are available. A version using common stock may be easier to source than a thickness chosen only in CAD.

For loaded supports or parts whose failure would have serious consequences, justify the choice through appropriate engineering. A prototype can check assembly and use but does not replace that justification.