How to Resize Quilt Blocks

Have you ever seen the 'perfect' applique quilt block, only to discover that the directions are for a 12" applique block but, would you need to make it fit in a 10 inch square? If so, these simple formulas will help you with that 'higher' math!

OK, I admit to being a retired computer programmer, so am a bit of a geek. I also used to be an accountant, so it is reasonable that I like numbers and I like for them to "come out". Quilting just enables me to play with color and fiber and making it 'come out'.

Even before I was a programmer, hubby (who is also a programmer) would repeat the drill "Source - Target". When you copy files from one directory to another, you are always moving the files from the 'source' to the 'target'. Same thing applies with resizing a block for the copier, whether you want the block larger or smaller. Only this time, the 'mantra' is reversed:

"what you want" (the target) divided by "what you have" (the source)

Begin with your goal it's the reason you have to deal with quilt math in the first place. What "you want" is a 10" block, so key in "10" into your calculator first. press the division (/) key, then enter the number "ya got," which is 12. Press the "=" key. The number 0.833333333334 comes up.

The copy machine wants a percentage, so move the decimal point to the right by two spots, and then you're done. Because this is a quilt, not a suspension bridge, you don't need all of the decimal points, so just ignore them. You need to reduce the 12" pattern by 83.3% to make a 10" block. Yep, it's that easy!

how to reduce the size of a quilt block

Let's work it the other way and make it a little more complex. You have this great applique pattern for a 6" x 7 1/2" whale, and you decide you'd like to make it at least 8" wide, but you're don't have a clue how tall that block will be.

Ask yourself, what is it you want? An 8" wide block. What do you have? A 6" wide block. 8 / 6 = 1.3333. This is called the "proportion number." Move the decimal point two places to the right, and you've figured out that you need to enlarge the heart pattern 133.3%. How tall will it be? In this case you multiply the original height (7 1/2") by the proportion number, which is 1.3333. So, 7.5 x 1.333 = 9.99975. The heart will be about 10" tall, (again, not building a bridge!)
how to enlarge the size of a quilt block
One way to check that you did the math correctly is to remember the following. The proportion number will always be greater than 1.000 if you're enlarging something, and will always be less than 0.999 if you want to make something smaller. Always. If you want to reduce a pattern but you have a proportion number larger than 1.000, you likely entered the wrong number into the calculator first.

Remember, "Ya start with what you want."

When changing the sizes of blocks, always do the proportion calculations with the numbers for finished sizes, not cut sizes. This is because you use different numbers to add seam allowances to:

    • 7/8" for half-square triangles (HST)
    • 1.25" for quarter-square triangles (QST)
    • 1/2" for Squares
    • 1/2" for rectangles.

Do all the proportion calculations for the finished pieces first, and then add the seam allowances.

Hopefully, you found this information helpful. And remember, to keep quilts in proportion, start with what you want, and divide it by what you've got. If you have questions or suggestions for future tutorials, just let me know.