Hem & Seam Calculator

Calculate material allowance for various sheet metal hem and seam types including open, closed, teardrop, and rolled hems.

Inputs

Material Thickness

Hem Type

Hem Length

Seam Type

Tab to move between fields

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.

How the result changes with Material Thickness

Material Thickness	Hem Allowance per Edge
0.69	2.76 mm
2.17	8.68 mm
3.94	15.76 mm
5.41	21.64 mm

What each input means

Material Thickness: Sheet metal thickness.
Hem Type: Type of edge hem to apply.
Hem Length: Length of the edge to be hemmed.
Seam Type: Type of joint seam if applicable.

How this is calculated

Worked example, using the default values

Identify Input Parameters
4 parameters
Material Thickness = 1, Hem Type = 2, Hem Length = 500, Seam Type = 1 = 4 input(s) provided
Calculate Hem Allowance per Edge
Hem Allowance per Edge
4 = 4
Calculate Seam Allowance per Edge
Seam Allowance per Edge
3 = 3
Calculate Both Edges
Both Edges
8 = 8

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