KestnutsIt's about 21 1/4". The 13" (12.99 actually) is the width at the front edge of the inner seat. This is a very comfortable chair because it does not have the hard bolsters of many gaming style chairs and the sides slowly rises up. I have sat it in myself since I got an advance sample in January of 2016.
KestnutsI've had this chair for awhile now and personally I will say the comfort is outstanding! I think the only thing that I must say is it does stand taller than most standard office chairs. For me that didn't make a bit of difference for my comfort, but I thought I should put it out there.