Woven fabrics are composed of two sets of yarns, one vertical and one horizontal.  The long or vertical yarns have a finished edge where you will often find the name of the company, the print name and the circles of colors used in the printing process.  The horizontal yarns are the cut edge of the fabric and they will ravel or fray.  To straighten the fabric we are putting the vertical and horizontal yarns perpendicular to each other.  This puts the grainline straight so the project you use the fabric for will lay straight, not curl around the body or in the quilt.  Along the selvedge or vertical side of the fabric there will be no stretch, the horizontal or cut edge will show some give when pulled.  The greatest amount of stretch will be on the bias, the diagonal line of the fabric.

Straightening your fabric would take place after you have pre-washed your fabric and before beginning to lay out and cut.

Step 1.  Finding the horizontal thread

Look at your fabric along the cut edge.  At the side that the yarns look lowest clip into the selvedge with your scissor about 1/2 inch up from the cut edge.

Find the horizontal thread and pull gently like gathering.  On the picture the thread is marked with a black line.  You will be able to see a line like a run in a knit fabric.  You will cut along that line as far as able, then pull the thread more.  If the horizontal thread breaks cut to that point and then work on the horizontal threads to get it again or another along that same line.  Continue this process across the width of the fabric.

Do the same to the other cut edge of the fabric.

Step 2.  Squaring up the Fabric

Fold your fabric lengthwise matching up the selvedges of the fabric.  When it is smooth you may have one edge of the fabric higher than the other on the edges you just pulled the horizontal thread.  Now you are going to straighten the grainline. This is done by gently tugging on the diagonal or bias line of the cloth.  You can do this better with a partner. Each of you will take the short end and gently tug to get the fabric in line.  Sometimes you need to move down the selvedge a little and tug there.  Periodically refold the fabric to be sure you are getting it to line up.  Fold it the same as at first with the selvedges lined up and fabric laying flat and smooth.  You may need to check and then tug some more to straighten. 

Question:  Why is my fabric crooked?

When fabric is folded and rolled onto the bolt it can easily be pulled off the grainline.  When purchasing fabric check this before having it cut from the bolt.  If your fabric is too far off it can be almost impossible to get on grain again.