Grain is the direction the threads run in a woven fabric, and cutting to it is what stops a garment twisting.
Three directions.
Lengthwise grain runs parallel to the selvedge. It is the most stable — very little stretch. Most pattern pieces are cut with this running vertically down the body.
Crosswise grain runs selvedge to selvedge. Slightly more give.
Bias is 45 degrees to both. Maximum stretch and drape. Bias-cut garments hang beautifully and are much harder to sew, because the fabric moves under the needle.
Why it matters practically. Cut a trouser leg slightly off-grain and the seam spirals around the leg after a wash. Cut a bodice off-grain and it hangs asymmetrically no matter how well it is sewn. Neither can be corrected afterwards.
How to get it right. Every pattern piece has a grainline arrow. Measure from the arrow to the selvedge at both ends of the arrow and make the two measurements equal. That takes ten seconds per piece and it is the single most skipped step in cutting.
Straighten the fabric first. Fabric comes off the bolt distorted. Pull it gently on the bias, or tear across the crosswise grain to find a true line, before laying out.
Questions people actually ask
Does grain matter on knits?
Yes, though it is called wales and courses rather than warp and weft. The principle is the same: the vertical direction has less stretch and should run down the body.
What happens if I cut on the bias by accident?
The piece stretches as you handle it and comes out larger and distorted. On a small piece you may get away with it; on a bodice you will not.
Last reviewed 2026-08-11