For convenience and economy I mat 10x14" prints with a 11x15 window. A small inconspicuous signature doesn't demand additional space at the bottom. Mats ordered in quantity can be used for portrait or landscape orientation. This might be inappropriate in upscale galleries, but works fine here in the boondocks.
Thank you everybody. I made my initial decision and sent in an order. I decided 1/2" all the way around except for bottom being 3/4" (float mat) and mat itself 3" all the way around except for bottom 3 1/4".
Played it safe by using small offset. Will see how it will turn out. It's so hard to decide....
I print about the same size as you and mat my prints at home. What I do is calculate the window opening 1cm (10mm ) bigger than the actual image, and then, add half a cm. in the bottom to add my initials just below the image in the right side.
Using centimeters or milimiters lets you be more precise and the logan mat cuter I use has both scales, and you save a lot of money cutting your own windows.
Well, my 8 x10 Ansel Adams print (vertical) has top mat top and side borders of 2 1/2" and the bottom 3 1/4 " and I quite like the proportions of it. If it was good enough for AA, it's good enough for me.