I gave the avatar away so don't have measurements. My latest:
http://www.quiltingboard.com/t-95959-1.htm#2414431 is 16 1/2" x 25" but is has narrower borders
Each block ends up to be approx. 2 7/8" so if a specific length is needed you can go from there or do the basic grid & add borders to get desired length.
FYI - pot holder is 2x2 grid with 3" border. Measures out to be 8"