# Quilt Blocks: Simple Math Part 3

We’ve been learning some basic quilt math and we’re up to Part 3. Are you still with me?!

If quilt math isn’t your strong point and you really want to wrap your head around these concepts, you might want to review Part 1 and Part 2.

What if you have a block diagram but no finished size and no patch dimensions? How do you determine how big you should make it, or how big you want to make it? This idea is similar to the ideas in Part 2, and yet different.

Let’s say you have the block photo above. Once again the first thing to determine is how many divisions there are across the block.

There are five, as you can see by the black lines I have drawn. Technically, you can make the block any size you want, but life will be simpler if you make the block so that each of the five sections is a nice round dimension, which will be rotary cuttable. Examples would be 1.5″, 2″, 2.5″, 3″ and so on. When you get up to about 4″, keep in mind that the block will be quite large, since 4″ x 5 sections is 20″. That’s a hefty block.

Let’s say you decide on 3″ per section for a 15″ finished block (that’s 3″ x 5 sections = 15″). Here are the patches you would need:

• 5 purple squares to finish at 3″ because they take up one section; add 1/2″ for seam allowance and you know to cut 5 squares 3.5″ x 3.5″

• 16 yellow squares to finish at 1.5″ because you can see they take up 1/2 of a section; half of a 3″ section is 1.5″; add 1/2″ for seam allowance and you know to cut 16 squares 2″ x 2″ (1.5″ plus .5″ is 2″)

• 16 purple squares 2″ x 2″ (same math as above)

• 4 each of green and yellow rectangles; you can see they are 1.5″ x 3″ finished so you add the 1/2″ seam allowance to both width and length and you get 2″ x 3.5″; cut 4 each of yellow and green rectangles 2″ x 3.5″

• Triangles: you can see they take up one section which is 3″. Add 7/8″ (we covered that in Part 2) and cut squares 3 7/8″ x 3 7/8″; cut 4 from yellow and 4 from pink/orange.

Look at the photo again: you see there are 8 yellow triangles and 8 pink/orange triangles. Why are we cutting only 4 of each? Because you’re going to cut them in half diagonally, which will result in 8 of each.

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This example of a 15″ block is pretty simple because the 5 divisions or sections divide equally into 15. You make life easier when you choose a block size that is divisible by the number of sections. In other words, this block would work well as a 5″, 10″, 15″ or 20″ block because those numbers are all divisible by 5, the number of sections in the block.

What if you really needed a 12″ block? Could you make this block finish at 12″? Absolutely you could, but the sections will not be an easily cuttable dimension because 12″ divided by 5 equals 2.4″—not so easily done with a quilting ruler. If you are determined to make the block finish at 12″, you’ll want to create templates. Quilt design software such as Electric Quilt’s EQ7 makes this a breeze. The templates would be funky dimensions, but with templates it doesn’t matter.

If templates send you screaming, another solution is to choose a different block that has a number of sections that divides neatly into 12, such as 2, 3, 4, or 6.

I think that’s enough quilt math for one day. We’ll dive more into the idea above in Part 4 next week.

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Put all that you’re learning into practice by checking out the Block Bonanza of 150 block diagrams in the March/April issue of Quiltmaker.

If you plowed through all this math and are still reading, you deserve a prize! Leave a comment by midnight Saturday, Feb. 23 and I’ll choose a winner for a little bundle of quilty goodness. Two winners! #3 and #14 have been notified by email. YAY!