The top and bottom chords are often different sizes. Some joists even have changing web bar sizes. Also, different manufacturers have used different strengths for chords and webs, different panel sizes, end panels, etc. Therefore, you cannot tell the size of the joist by simply knowing the chord sizes and web.
The best ways to determine the joist size is to obtain the tag or the plans or the shop drawings.
in my copy of the 60 year SJI manual, there is a page (page 11) showing information to assist in joist sizing based on chord sizes. However, it is for SJ, S, S, J or H series joists, not K series. The table doesn't have anything for a joist with a top AND bottom chord of the size you listed. Also, the table doesn't include info about the webs.
Jike is correct, a tag is the best way to determine the size. from time to time, I've had a Vulcraft rep visit the building and help. that's not always possible, but if you have time for that it helps.
