Reddit mentions of Libbey Glassware 15238 Gibraltar Beverage Glass, Duratuff, 12 oz. (Pack of 36)

I analyzed the photo and it is approx. 41% off the table.

See for yourself:
https://i.imgur.com/lWTsn3S.jpg

-------------
Above the line is the original comment in the state it was gilded in for the context of a future reader, however, further analysis (seen below) has shown it is actually only approx. 38% off the table, the 41% figure above will remain for archival purposes.

BIG EDIT:
/u/TheScotchEngineer wanted the calculation done by area as opposed to length so as to be more optimistic as to the amount on the table, this followed:

If you do it by area you would have to know the dimensions of the glass itself.

Which is possible with some minor assumptions.

http://www.globalindustrial.com/p/foodservice/pizza-supplies/pizza-stands-risers/salt-pepper-shaker-1-5-8-oz?infoParam.campaignId=T9F

Ok, those are the salt shakers in the picture, which have the following dimensions:
HEIGHT INCHES 3
WIDTH INCHES 1.25
DEPTH INCHES 1-1/4
CAPACITY OUNCES 1-5/8

Since all of this stuff is generally going to be coming from a restaurant supply, we can locate the design of the glass and then make sure it scales correctly to the salt/pepper shaker.

So these glasses in particular are a 12 oz. Libbey Gilbraltar style, which is known because of the height of the glass given in relation to the height of the salt shaker, and the particular design styles of each.

http://www.amazon.com/Libbey-Glassware-15238-Gibraltar-Beverage/dp/B002RC545U

Overall Height 4.875 inches
Overall Length 3.25 inches
Overall Width 3.25 inches

However those width/length measurements concern the overall glass, not just the bottom. So using the height of the salt shaker as a reference and already having known the -overall- length of the glass it was possible to determine that the base of the glass is actually 10-13% smaller (approx.) than the listed length.

That said, it's likely that the bottom of the glass is around 3 inches in both length/width, and not another number due to that being a more standard result to measure for production.

So calculating for area, 3.1415926535(r)^2, where r=1.5in yields 4.712 in^2, or 4.71 in^2 when rounded down.

Using the determined length of the bottom of the glass based on the amount of that length from the edge, and based on the size of the area, it can be concluded that the glass is 62% on the table, and 38% off the table, by area.

Or, in other words, the glass is roughly 2.92 inches^2 by area on, and 1.79 inches^2 by area off*.