One fabulous reference book I use all the time is: All-in-one Quilter's Reference Tool by Harriet Hargrave, Sharyn Craig, Alex Anderson and Liz Aneloski. Amazon has it for $11.38 here: https://www.amazon.com/All-One-Quilt...e+tool+updated It has a wealth of information to bed sizes, adding sashing, changing to on-point and sizing setting triangles to name just a few. Well worth it IMHO

When I did a block of the month, I ended up with 13 blocks. They work out perfectly on point to produce a square piece. Put 9 of the blocks on point in 3 rows of 3. There are now 4 holes. Put the other 4 in those holes and you have it.

Think of our flag. There are 5 rows of 6 stars which makes 30. Then the other stars are fitted into the holes between all these. There just happen to be 20 of those holes. 30 plus 20 = 50.