Explanations of four popular quilt block layouts:
Four-patch and nine-patch quilt blocks are routinely sub-divided to create more intricate patterns, but once you become a block-watcher it will be easy to identify their underlying structure. Five-patch and seven-patch block grids can be sub-divided into multiple-patch units, but it isn't common, other than half-square triangles, since the grids are usually a bit small already.
Keep in mind that individual grids in a quilt block are sometimes combined, rather than subdivided, like the areas created by red strips in the five-patch block above right.
Why should you care about block structure? Because once you can decipher a block's grids, you can make it larger or smaller with ease. And although structure is important for altering the size of a quilt block, it's also a huge component when designing a quilt, because some blocks just don't 'mesh' when sewn side-by-side, even if they're the same size. You'll learn more about that in my patchwork structure tutorial.
Always make a test block in the new size, or for any pattern, before cutting all of your fabric.
If you find a block that isn't easy to alter using the methods in this tutorial, make a photocopy, enlarging or reducing the block to the finished size you wish to sew. Measure the sizes of its patches (remembering that the dimensions are unfinished). Use templates to construct the block or refer to the patchwork shape cutting instructions to choose a patch and block size that can be easily rotary cut (remember that all shapes must be altered in the same way).