My bars are 14.5" long, but with sitting on the sides, about 13.5-13.75 is 'usable' by the bees. Like Bjorn, have read that anything much longer and comb damage, and straight comb (comb attached to only one bar), becomes an issue.
Did work another TBH that was probably 20" or more wide. Much of the comb was curved, spreading out to multiple bars, which made it very difficult to work. And the ones with honey were VERY heavy. Unfortunately, I broke a lot of it because it spread to multiple bars. I haven't seen it since, so I hope they were able to rebuild over the summer. I felt very badly.
The width of the bars vary. Most are 1.25". However (from learning here and Michael Bush's site), the bars toward the back, where the bees build comb to store honey are 1.5" wide.
Have not weighed them. First year into it, and I'm leaving the honey for them over winter.