According to the math, an inch in extra width each tire; half of that will project inward and half outward. So, all things otherwise the same, you’ll gain a 1/2” on each side for a total increase of 1” in overall width.
In the real world, it matters which tires are involved, because manufacturers fudge the numbers all over the place. So all 11” wide on paper are not necessarily the same width. You could start by looking at the specs for section width from the manufacturer and see how the actual section compares to the nominal size.