Quilting is all about measurements. When you get them right, your quilt
goes together like the pieces of a puzzle. If you mess them up, you have
trouble from start to finish.
One of the things that often confuses new quilters is "raw" vs. "finished"
measurements. It is vital that you understand the difference.
When you follow a pattern, and it tells you to cut a piece of fabric, that is
almost always a "raw" measurement. That is because the measurement
includes the seam allowances.
"Finished" measurements are the width of blocks or fabric after it is sewn
together. Since you cut fabric pieces with a 1/4 inch seam allowance on
each side, the "finished" measurement is almost always 1/2 of an inch smaller.
When I was selling fabric squares on ebay, I sold them 4 inches wide. I
chose that measurement because that is what everyone else was selling at the
time. People who have been quilting for awhile know that 4 1/2 inches if
much more versatile.
Some of my buyers got confused, thinking that the squares were going to measure
4 1/2 inches, and that the seam allowances were "built in."
It is easy to plan quilt if you make your strips and blocks 2 1/2 or 3 1/2
inches. All you have to do is remove the 1/2 inch to easily figure out the
finished width of the quilt. That is why you see so many jelly rolls at 2
1/2 inches. That is also why many people cut up their fabric scraps at 1
1/2 or 2 1/2 inches.
When following quilt patterns, reading quilting instructions, or just planning
your own quilt, be sure you are following the directions clearly by always
knowing if you are reading raw or finished measurements.