WHAT IS IT?
The grain line is a printed line on pattern pieces that marks the lengthwise grain, also called the straight of goods or straight grain. It’s usually marked with an arrow. This line is used to help align your pattern pieces on your fabric so that they are cut on grain. The grain is the lengthwise direction of your fabric, running parallel to the selvage. Think of a vertically striped fabric, where the stripes go up and down the fabric. That’s what the grain line would look like if you could see it.
Opposite to the lengthwise grain is the crosswise grain. The crosswise grain runs across the width—that’s an easy way to remember the difference.
Garments cut on grain will hang straight along the lines of the body, while garments cut off grain may twist around your body or hang unevenly. Sometimes the grain line will appear as a “cut on fold” marking on the pattern piece. This marking is directing you to fold the fabric on the straight grain and then line up the edge of this piece along the fold of the fabric. When you cut it out, you’ll end up with a mirrored piece with the centerline aligned with the lengthwise grain.
Pattern placed on grain line
Grain line with “Cut on fold”
WHEN DO YOU USE IT?
You’ll use the grain line every time you cut out pattern pieces from fabric. Every pattern piece is marked with a grain line or a cut on fold marking. The grain line is also helpful when placing pieces on the bias (page link). If you are cutting striped (page link) or plaid (page link) fabric, the grain line will help you to line up the stripe and plaid lines.
Take a look at the striped fabric above. Striped, plaid and other vertically printed or textured fabrics make it easy to see where the grain line is. See how the grain line arrow is parallel to the direction of the stripes?
When you see diagonal stripes or plaids, it usually means the fabric is cut on the bias. True bias refers to a 45° angle from the grain line—exactly halfway between the lengthwise grain and the crosswise grain. See page link for more on the bias. On your pattern pieces, the grain line will be marked with a diagonal line to indicate cutting on the bias.
HOW TO LAY OUT FABRIC ACCORDING TO THE GRAIN LINE
Look at the fabric-cutting diagram and find the one for the garment you’re making. Sometimes there will be one fold; sometimes there will be two folds with the selvedges (page link) folded into the middle. Or sometimes there are both types of cutting layouts for a single view.
Fold the fabric in half according to the cutting layout. Line up the selvedges so they are even, and smooth out any wrinkles.
Place your pattern on the fabric. Rotate the pattern piece until the grain line is parallel to the selvedge or to the fold. Don’t worry about having it exactly parallel yet; you’ll fix that in the next step.
Starting at one end of the grain line arrow, measure from the arrow to the fold or selvedge, whichever is closer. Note this measurement. Pin the pattern in place next to the grain line arrow.
Measure from the opposite end of the grain line arrow toward the same fold or selvedge. You want this measurement to be exactly the same. If it is, then your garment piece is cut on grain. Rotate the pattern piece until the measurement is the same at both ends of the arrow.
With these two points pinned at each end of the grain line arrow, the pattern piece is aligned with the lengthwise grain of the fabric and you’re ready to pin the rest of the piece in place.
Source : The Sewtionary An A to Z Guide to 101 Sewing Techniques + Definitions
About the Author : Tasia ST. Germaine