For making any quilt larger, you have to know how many extra blocks you need. Normally that could be as simple as adding an extra row and column - kind because the column has to take into account that extra row. But this quilt has the blocks set on point so it is a bit more complicated. You have to figure not only the full blocks but the half blocks along the sized plus the quarter sized blocks that go in the corners
Once the number of extra blocks is known, then the number pieces (squares, rectangles, full, half and quarter triangles, etc.) that make up the block can be calculated. From those numbers the amount of fabric in square inches or millimeters is created. And finally, the yardage can be determined.
Now, with my engineering background, doing this math, using Microsoft Excel for the calculations (not taking any chances especially since I am dyslexic) is easy for me; you might think --
WTF, I don't even know where to start to do all that math!!!
Have no fear, there are books for this!!
Go to your favorite on line book seller and enter "quilt math" and over 2 dozen books will be listed. This is my favorite which I bought in the 1980's and is still published today - Taking The Math Out of Making Patchwork Quilts.
Its a great book that covers, straight and on-point sets, mattress sizes and quilt sizes for them; adding sashing, borders and more. Then it becomes easier to know the number of blocks and the yardage.
I would like to also mention that there are some websites that have quilting calculators.
Before using the books or a calculator, take a quilt pattern and run the numbers for a know size and verify the numbers align - remember the pattern may round up the yardage required.