Below I have listed several math calculations that would be useful to a quilter.
Calculate the diagonal of a quilt block
To calculate the diagonal of a quilt block when setting blocks "on point" -- Use your calculator -- punch in 2, punch the "square root" button = 1.4142 then without clearing the calculator, punch the inch measurement of the block size. Example a 14" block on point would be calculated as follows. Punch in 2, then the square root button x 14 = 19.8. You can then round the decimal down to 19 3/4 inches.
Calculating meters to yards and yards to meters
Do you ever purchase thread that is measured in meters and wonder how many yards it is? Or are you using a pattern that is written in metric? There are 39.37 inches in a meter -- a meter is 3.37 inches larger than a yard.
Here is the formula to calculate meters to yards.
Punch this in your calculator - # of meters x (times) 39.37 / 36 = # of yards
Here is the formula to calculate yards to meters.
Punch this in your calculator - # of yards x (times) 36 / 39.37 = # of meters
For example -- I recently purchased thread with 1000 meters. 1000 x 39.37 / 36 = 1093 yards of thread on that 1000 meter spool of thread.
Calculate the circumference of a circle
You will need the circumference of a circle to estimate the amount of bias binding you will need to cut when making a round quilt.
Circumference = Pi x d . In quilters terms this is pi (pronounced pie) x diameter. Diameter of a circle is the measurement across the widest part. Think of your circle as a pie. The diameter is the line across the pie when you are cutting it in half.
Pi = 3.1415928 -- for the sake of quilting you can simply use 3.15 instead of that long decimal number. Use your calculator -- punch in 3.15 times (x) the number that is the diameter of your round quilt. That is the number of inches of binding you'll need to allow for the binding of your circular quilt.
The Golden Mean
The Golden Mean is a rectangle used by mathematicians and artisans for centuries. It is an 8:13 ratio. This rectangle is pleasing to the eye and many art quilts are based on these figures. A credit card is sized using the Golden Mean. They want the shape of the credit card to be pleasing to us so we will buy more fabric and quilting supplies with it.
To decide the size rectangle you will want for your quilt, you will need your calculator.
If you know the width you would like for your quilt -- multiply width by 1.625 to get a pleasing length. If you know the length you would like for your quilt -- divide length by 1.625 to get a pleasing width.
Enlarging and reducing on the copy machine or computer scanner
Many patterns in magazines, books and online are available in a reduced form. Most of them tell you the percentage to enlarge each pattern piece or foundation pattern.
Some books or patterns do not give you a percentage, they just print the pattern pieces on a grid and tell you to enlarge the grid to 1" squares or 2" square or whatever.
There is a very useful tool available at art supply stores, some quilt stores, and in some online quilting sites. It is called a "Proportional Scale". It is a circular plastic wheel with numbers and percentages around the perimeter.
The proportional scale has two plastic circles riveted together at the center. The smaller inner circle has numbers printed that give the "size of original". It also has a window that shows the percentage of original size and the number of times of reduction. The outer circle is the "reproduction size".
Example of how to use this tool
To enlarge - If you have a 7" quilting design and you would like it to be 10" you simply find the 7" marking on the "size of original" wheel and rotate this wheel until the 7" mark is lined up with the 10" mark on the "reproduction size" wheel. Look in the window and you will see the arrow pointing to 142%. That is the number you program into the copier or scanner to make your enlargement.
To reduce - If you have a 7" quilting design and you would like it to be 4 1/2" you simply find the 7" marking on the "size of original" wheel and rotate this wheel until the 7" mark is lined up with the 4 1/2" mark on the "reproduction size" wheel. Look in the window and you will see the arrow pointing to 64%. That is the number you program into the copier or scanner to make your reduction.
This tool works really well and sells for approximately $5. It is well worth the investment. Many copy shops will do this for you using their "proportional scale" tool but they will charge you for each time they use it. This tool will pay for itself in only a few visits to the copy shop.
Quilters math or arithmetic is not frightening. The answers to all the above "math problems" are merely a matter of knowing a formula and using your calculator.