Quilting and the Raw and Finished Quilt Block Measurements
There are two words that must never be confused when it goes to cutting and piecing a quilt block. Those words and raw and finished.
These words are so important to accuracy, that you will find them bolded on every page on this site. One of the most important concepts to grasp when it comes to measuring for quilt blocks is the difference between a raw and a finished size quilt block.
This can be confusing to the beginning quilter. If you forget about it, it can mess up even an experienced quilter.
Every piece of fabric that you cut for piecing is going to have a seam around each outer edge. Since all seams in quilting are 1/4 inch, and each seam uses two pieces of fabric, you lose 1/2 an inch with every seam you sew.
If you are making a quilt with square blocks that you want to finish at 6 inches, they need to be cut at 6 1/2 inches raw.
So 6 1/2 inches is the raw size of the square. 6 inches is the finished size of the square. Some patterns do not make this clear, and it can be confusing.
You can get confused when you purchased pre-cut quilt blocks as to whether they are a raw or finished measurement. I've seen this confusion on auction sites such as ebay. Some people order 4 inch quilt squares, thinking the seam allowance in "built it." They received 4 inch raw squares, when what they wanted was 4 1/2 inch raw squares.
Another thing to note is that in order to make measuring easier, a lot of patchwork is done with 4 1/2 inch raw squares, and 2 1/2 inch raw strip piecing. I call this Simple Measurements.
Simple Measurements make quilting both easier and more frugal. Be sure and read about this concept.
Be sure that you understand to always think raw and finished when you are planning the sizes of your quilt blocks and projects.