These are the generally accepted standards for WPI. I actually classify my lace as yarn that has 20 or more wraps per inch, and cobweb to be anything 25 or more wraps per inch.

WPI Yarn Type YPP
18+ Lace 2600+
16-17 Fingering/Sock 1900-2400
13-15 Sport 1200-1800
11-12 Worsted 900-1200
9-10 Bulky 600-800
< 8 Super Bulky 400-500