Hemming Calculator

Hemming allowance is the extra fabric folded under (and usually sewn) to create a clean, finished edge on garments. The correct allowance depends on the fabric type, hem style, and garment use.

Hem Allowance Formula:

Cut Length = Finished Length + Hem Allowance + Seam Allowance (if applicable)

Standard hem allowances by garment type:

Double-fold hem (most common for clean finish): Half the allowance turns under twice, so the allowance is always double the hem you end up seeing. A 2-inch allowance gives a 1-inch finished hem: fold up an inch, fold up an inch again, and the raw edge is buried inside where it can never fray. That is the number to watch, because a 1.5-inch allowance sounds generous and finishes at three quarters of an inch, which on dress trousers looks skimpy.

A single fold uses the whole allowance in one turn, so it needs the raw edge serged, bound or pinked first. It is the right choice on heavy denim, where a double fold puts four layers under the needle at the side seam.

Worked example, hemming trousers: Client inseam needed: 30 inches Current inseam: 34 inches Amount to remove: 34 − 30 = 4 inches Allowance needed: 1.5 inches Cut at: 30 + 1.5 = 31.5 inches from waistband seam The extra 2.5 inches is trimmed away.

Fabric-specific tips:

• Heavy denim: use a denim needle and reduce the allowance to 1 inch, because too much bulk at the fold shows through as a ridge
• Chiffon / silk: use a narrow rolled hem of a quarter inch. A heavier hem weighs down light fabric and makes it hang crooked
• Knit fabrics: use a twin needle or coverstitch to allow stretch in the hem without breaking thread