It's All About the Numbers
Aren't you glad that published patterns tell you exactly how to cut each of the patches in your quilt? If you have constructed your own designs, you know what it takes to come up with the numbers! Whether the pattern is going to be published or not, you've still got to do the math. First you have to decide how you want to construct the sub-assemblies of your blocks. Then what you need to cut (squares?, triangles?, strip sets?....). Then how many of each shape you need, how many can you get in a strip, how many strips, what amount of fabric do you need. Are you going to use a template? Do you need extra fabric to fussy cut - how much? Aarrgghh! But it all has to be done.
So do it as carefully and accurately as possible. Check and double check. A mis-calculation can lead to wrong cuts, wrong sizes, needing more fabric, not being able to find it, starting over, or making do. So, persevere, my friends. Resort to an electronic spreadsheet! I have a spreadsheet called Binding Calculator. It not only computes yardage for binding based on width of fabric and width of binding, but it computes the yardage for backing, the size of the backing pieces to cut, and a mirad of other things that I've run into over the years. Most recently it has told me how many strips of each fabric of a strip set I will need.
Quilting technology has come a long way. From paper and pencil, to spreadsheets, to quilt design software. Frankly, I don't know how our fore-sisters did it all by hand without going a little nuts. I am in awe of their creativity, resourcefulness, and intelligence.