What's the proper way to punctuate inches when recording the dimensions of something?

When punctuating the dimensions of something, if both dimensions share the same units, does the punctuation occur after each measurement or just after the last one. For example, if I'm looking at a sheet of paper, which is correct: {8 1/2 x 11"} or is {8 1/2" x 11"}?

You want to use the punctuation after each number. Otherwise you may get confusion on the first number - not just about feet vs. inches, but also because it's common notation to write

(number) x (thing)

to indicate quantity and it may be read as "8 of the 11 inch widgets".

Also this may be personal preference but decimal is much easier to read than fraction for measurements, e.g. 8.5" x 11" instead of 8½" x 11"