# Quilt Math and Drafting Part 1 - squares, rectangles and half square triangles

First, some definitions. A

**block, square or HST is one that is sewn onto other fabric on all four sides. It is the size you want the piece to be when your quilt is***finished**finished*.**measurements include enough extra fabric for seam allowances. So our blocks are 12.5 inches square***Unfinished**unfinished*and 12 inches*finished*.Why did I choose for our blocks to finish at 12 inches? First of all, the bigger the block, the easier it is to sew. Since we are working with new techniques I figured we could give ourselves a break. :) But almost more importantly a 12 inch block is

*very*versatile.Let's say I wanted to design my own block and I want to have the block divided into 4 columns and rows. 12 divided by 4 is 3, so each square in my block has a finished size of 3x3 inches. I start sketching and divide the middle 4 squares on the diagonal and make a pinwheel design.

But it needs something more so I color in some squares radiating off from the pinwheel. Looks good! But I notice that the two white blocks on the sides could be combined. No point sewing two pieces of fabric together when you can just cut one, so I sketch the block again leaving out the lines that divided the two squares.

Here are the different pieces that I will need.

Now I need to figure out how large to cut my pieces. I know that each finished square is 3x3, the finished rectangles are 3x6 and the finished HST measure 3x3.

I will need to have a 1/4 inch on each side of the square and rectangle for the seam allowance. The finished height of the square + 1/4 inch on top + 1/4 inch on bottom = finished height + 1/2 inch.

The same holds for the width of the square and rectangle. Finished width +1/4 on the right +1/4 on the left = finished width +1/2.

The rule is to add 1/2 inch to the finished length and width of squares and rectangles in order to find the unfinished size that you need to cut out. So I would need to cut my square 3 1/2 x 3 1/2 inches and my rectangle 3 1/2 x 6 1/2 inches

**Squares and Rectangles - add 1/2 inch to length and width**

A HST unit is made out of two right triangles. Each triangle needs it's own seam allowance.

I will need to cut squares 7/8 inch larger than the finished HSTs. In this case the squares I would use to make my HSTs would be 3 7/8 x3 7/8. If I planned to trim my HSTs to size I would cut my squares slightly larger, 4x4 inches.

**Half Square Triangles - add 7/8 inch to the length and width of the squares you use to make them**

**(add 1 inch if you plan to trim to size)**

Clear as mud?

To finish my block I would count up how many different shapes I needed.

4 light 3 1/2 x 6 1/2 inch rectangles

4 medium 3 1/2 x 3 1/2 inch squares

2 dark 3 7/8 x 3 7/8 inch squares

2 light 3 7/8 x 3 7/8 inch squares (or 4x4)

I would make my HSTs, attach them to the medium squares, sew the rectangles onto the sides and then join the four subsections into a whole block. And voila! My block would be done.

I know there is way too much math and way too few pretty pictures in this post. :) Please, if you have any questions let me know.

I have an optional challenge for you this week: design and make your own 12 inch finished block!

Sketch a large square and divide it into 4 sections length and width wise, just like I did. Now start sketching. You can use squares, triangles and rectangles. Here is a series of 4x4 blocks that I did to come up with ideas for a bee block. It doesn't have to be pretty! :)

Sketch a large square and divide it into 4 sections length and width wise, just like I did. Now start sketching. You can use squares, triangles and rectangles. Here is a series of 4x4 blocks that I did to come up with ideas for a bee block. It doesn't have to be pretty! :)

Really, the possibilities are endless.

Feeling up to the challenge? You Can Do It! I would love to see what you make! (Flickr group here.)

Be sure to leave a comment on the next post to be entered in the "I've Made All 3 Blocks!" giveaway.

Be sure to leave a comment on the next post to be entered in the "I've Made All 3 Blocks!" giveaway.