Hem & Seam Calculator
Calculate material allowance for various sheet metal hem and seam types including open, closed, teardrop, and rolled hems.
Inputs
mm
mm
Results
Hem Allowance per Edge
4 mm
Seam Allowance per Edge3 mm
Both Edges (Hem)8 mm
Hem DescriptionClosed/flattened hem — edge folded completely flat
Seam DescriptionLap seam — simple overlap, spot-welded or riveted
Max Thickness for Hem Type1.5 mm
Total Hem Material2
How to Use This Calculator
- Enter material thickness and select the hem type (open hem, closed/flattened hem, or teardrop hem).
- Review the additional flat length needed for the hem and the minimum bend radius for the hem operation.
- For closed hems, account for the hem return width in the flat pattern.
- Use the flat length addition in your blank sizing calculations before cutting.
- Open hems are easier to form and safer on sheet edges -- closed hems provide more strength and a finished look.
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