Need some help in calculating please!
 

I need to make some blocks similar to the below - finished size 10 X 16 so unfinished 10-1/2 x 16-1/2. I would like to make these similar to the technique in HST's where you align 2 (right sides together) up, seam diagonally corner to corner 1/4 " on each side of the center of that, then cut on the center line and end up with 2 units. BUT I don't know how to calculate what sizes my initial cuts should be to get the result I need.
Can one of you please help me ? Ultimately I just need to know the dimensions but the formula would be awesome :)
Thanks in advance.

(This is a rough sketch, i know I probably didn't get all my lines in exactly the right spot but I hope you get the idea :) )
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I am watching to see the answer as I am also math challenged. my best guess would be to add 7/8 but with that wonky triangle i would bet you have to add more.

I just tried it and it does not work the pieces after sewing look like a kite shape i will try to see if I can take a pic took the pics and as usual can not find them on the computer

Yep Nancy - I just tried the same thing with paper...it does look like a kite lol. drats. but thank you!

I only know of two ways to make that rectangular unit - possible three:

Sew strips together and then cut out the unit.

Sew two triangles together. Be sure to mark the end points of the seams - match them up before sewing -you will have tails sticking out when the triangles are correctly lined up.

Paper piece.

The way you want to do it - you get the kite piece as sewwhat85 just said.

double drats! Thanks bear. I had this idea for a quilt back - i think i'll go for another idea now lol.

Had this same problem a few weeks ago. I gave up on the pattern. I found this while seqrching for a solution.

http://www.quiltdesignnw.com/PDF/HRT_2x4.pdf

tapper, I like your link.

The half square triangle formula won't work because the finished unit is a rectangle. EQ says to cut strips for those patches at 17-1/8" x 10-11/16", then slice in half along the diagonal to create the two right triangles. If you want to construct the block by sewing two rectangles together, I would bump the dimensions up to 17-1/2" x 11" and cut two rectangles that size out of scrap, sew them together, cut down the middle, press and then see how big the unit is. You may need to sliver trim to achieve the 10-1/2" x 16-1/2" unfinished size, or increase the dimensions of your rectangles until you get there.

The link provided contains some great information. I saved it -- just hope I can find it again when I need it!