bearisgray

If you want to cut rectangles diagonally for the side triangles of a triangle in a square -

You need to cut them 1-1/4 inch longer and a "scant" 3/4 inch wider

Example:

If the finished base size of the triangle is two inches and the finished height size is four inches:

Cut the rectangle 2-3/4 x 5-1/4 inches.

The center triangle:

Add approximately 7/8 inches to the width and approximately 7/8 to the height.

Example: Four inch "finished" base size and four inch "finished" height size:

Cut a strip 4-7/8 wide and the base will be 4-7/8 wide.