When your blocks come out at different sizes, the tidiest way forward is often to bring the smaller ones up to meet the largest rather than cutting anything down, and narrow framing strips, sometimes called coping strips, do exactly that. The maths behind them is more logical than it first looks. Start by finding the difference between your largest block and your smallest, since the largest is the size every block now needs to reach.
Take that difference and split it between the two opposite sides that will carry the first strips, so half of it is added to each side. Then add back the half inch that each strip gives up to its two seams. If your largest block measures twelve and a half inches and your smallest twelve, the difference is half an inch, which is a quarter of an inch to each side, and with that half inch of seam added you would cut those side strips three quarters of an inch wide. The side strips go on first, before you go anywhere near the top and bottom.
Only once those side strips are attached do you measure the block again to work out the length of the top and bottom strips, because that second measurement does not exist until the first pair is sewn in place. And measure it you must, every single time, rather than trusting the number the arithmetic handed you. Blocks that have been pressed and handled and shuffled around a design wall rarely sit at the size the pattern promised, and the ruler will always tell you the truth the calculation only guessed at.
The same idea, a narrow strip doing structural work between two blocks, is how blocks are joined in quilt as you go, except there the strip covers the seam on the front and on the back at the same time.
Which do you reach for when a block comes up short, building it back to size with coping strips, or a method of your own you have worked out over the years? I would love to hear how you handle it.
