Grading means trimming each layer of a seam allowance to a different width, so the layers finish in a staircase rather than all at the same point. The purpose is to stop a visible ridge on the right side.
Why the ridge happens. Two or three layers of allowance all ending at the same line make a hard edge inside the garment. Press the seam and that edge prints through to the outside, particularly on smooth or light fabric. It is one of the clearest signs of home sewing, and it is entirely avoidable.
The method. After sewing, trim the layer that will sit nearest the outside of the garment to the widest measurement — say 10 mm. Trim the next layer to 6 mm, the next to 4 mm. Interfacing gets trimmed shortest of all, or trimmed out of the seam allowance entirely before sewing.
The layer nearest the outside stays widest. It cushions the narrower ones underneath so their edges cannot print through.
Where it matters most. Collars, cuffs, facings, waistbands, welts, lapels — anywhere layers are enclosed and then pressed.
Combine it with clipping and notching on curves. Grading deals with thickness, clipping deals with curve. They solve different problems and most enclosed seams need both.
On very heavy fabric, grade more aggressively and consider trimming the interfacing out of the seam allowance before you sew.
Do not grade seams you may need to let out later. Once trimmed, the fabric is gone.
Press well afterwards, over a ham for anything shaped.
Questions people actually ask
How narrow can I go?
Around 3 mm on the innermost layer of stable fabric. Less than that and it frays out of the seam.
Do I grade every seam?
No. Only enclosed seams with several layers. An ordinary pressed-open seam has no layering to grade.
Last reviewed 2026-08-11