You'll need a proportional scale (or a calculator) to accurately reduce or enlarge quilt blocks patterns to fit a particular project.
The chart (there is a free downloadable chart for you further down on this page) can be used to identify the percentage to reduce or enlarge quilt block patterns on a copy machine without doing any math.
You'll need to know the size of the finished block (or pattern) that you have and the size of the finished block (or pattern) that you want.
Then find the percentage in the proportional scale chart.
For this example, the pattern you have for is for a 12" finished applique block, but you really want a 10" block.
Regardless of the method you choose, the percentage will be less than 100%. If it's not, you'll be enlarging the pattern instead.
Locate the 'size of the block you have' (12") in the left hand column of the chart. Now locate 'the size of the block you want' (10") in the top row.
At the intersection of this row and column you'll find 83%. (Most Xerox machines take only whole numbers--no decimals--so all the numbers in our Proportional Chart are rounded to the nearest whole number.)
Enter 83% into the Reduce/Enlarge area of the Xerox machine so that your 12" block would print at 83% or about 10". I highly recommend that you double check the finished block size before you leave the copy shop to ensure that it fits given that we've rounded those numbers.
On your calculator enter the size block that you want—or 10 inches. Then divide by the size block that you have—or 12 inches.
10 divided by 12 = 0.833333
To turn this into a percentage drop off all but 2 decimal places and multiply by 100...
0.83 times 100 = 83%
Enter this percentage into the copy machine and print your block.
I'll use a different example this time. Now you have a pattern for a 6 inch block, but you want a 9" one.
Regardless of the method you choose, the percentage will be greater than 100%. If it's not, the math is wrong.
Again, locate the size of the pattern you have or 6" in the left hand column. Next locate the size you want or 9" in the top row. At the intersection of this row and column is 150%.
Enter 150% into the Xerox machine for reducing/enlarging and print. Your 6" block will print at 150% or about 9". Again, double check with a ruler before you leave the shop.
The size of the block you want divided by the size you have or...
9" divided by 6" = 1.50
Multiply by 100 to turn this into a percentage...
1.50 times 100 = 150%
Enter 150% into the appropriate prompt in the copy machine and print.