These are some of my washcloths...they are all exactly the same size.  They stack nicely on the shelf.  

They are all made by me....because I hate to pay almost as much as for a washcloth that I do for a towel, especially when my son uses them to wash his car, wipe dog poop off his shoes, and clean up spills on the floor. So I can't see paying $4 for a washcloth for those chores!
So when a towel starts to wear out, gets stained or has a hole in it, I recycle it into anywhere from 6-8 washcloths.  First of all I cut off the end where the decorative band is.  It tends to shrink more than the rest of the towel and I don't like how it is puckered.  I use my rotary cutter and ruler and make short work of it all!
I cut 10.5" squares.  Later I will round the corners when I stitch the edges.  
I was able to get 6 squares out of this towel.  
Next I am going to bind the edges with my serger.  If you don't have a serger, you could use an overcast stitch to stitch the edges.  If you use a regular machine, you will need to round the corners prior to stitching. 
I start on one corner and serge all around the edge, 
rounding the corners as I go.
Here is the finished product...they will be a bit ragged until they are washed a few times.
I love that thread...this was the first time I had used it.  It has a heavier weight feel to it, not quite as thick as quilting thread, but thicker than regular sewing thread.  And it was only 97 cents at JoAnn Fabrics.  Usually I use white thread, once I used a rayon embroidery thread, but it didn't last very long.  
Here they are stacked on the bottom of my washcloth shelf.  I always buy Martha Stewart towels so the well worn towels make nice thick but soft wash cloths!  
