Hmm... Lego is metric:

"4.9152 cm is the volume of an 8-stud LEGO brick. It measures 9.6 x 32 x 16 mm."

So, the width of each peg element is 8mm, ~1/3", so a 3x3 block (which I've never seen and probably isn't made) would be approx. 1" x 1" x 3/8". A 4x4 block would be 1.25" x 1.25" x 3/8". But again, I don't recall having seen this either. But! If you look at the toddlers version of lego - the smallest single block in that range is the same as a 4x4 regular block, but taller. They are 1.25" x 1.25" x 3/4" according to my trusty tape measure.

PS. There is such a thing as a free lunch. We had one at the Boston Empeg Meet. Thanks ithoughti.