I have measured hundreds of fabrics (yes, really!) before and after washing them.
In my experience, fabrics do not shrink at the same rate. Assuming a 42-45 inch width of fabric - i have had some shrink up to 2.5 inches in width or length (per yard). Most only shrink about an inch in one direction or the other. Very few have little or no shrinkage, and I think one stretched a tiny bit.
Most of the fabrics I've washed shrink mainly in either length or width.