Specifically, the width of where my thighs are likely to touch the seat bucket sides. The width of the FRONT of the seat where your butt goes.
I am asking because I've looked it up and I keep seeing 17". such as:
Backrest Width (shoulder level) 19 inches (48.26cm)
Seating Area Width (total) 21 inches (53.34cm)
Seating Area Width (point of contact) 17 inches (43.18cm)
Recommended User Height 5'6"-6'2" / 170-190cm
Recommended Weight <299 pounds (108.4cm)
(pasted from Toms hardware, and other sources as well)
however, if I look at the Razer At a Glance, it appears to be 395mm, which is only 15.5".

so which is it? 15.5" seems quite narrow but 17" seems very reasonable.
Sorry again for the redundant questions...like I say, I've seen it asked quite a few times.