If you're in FW I suspect Pulliam installed your pool. Would be worth calling Pulliam & asking. Then you could get all the specs on your equipment etc. It was the specs that told me it was 60 sq. ft. I don't believe it was on the filter anywhere.
steph, look at the bottom right corner of the label in your pic. See the hole punched out at the bottom, the second from the left? Look at the column above this hole and that should tell you the specific model # as well as the specs.
Now that you know the model, it might be possible to google up an online owners manual. I was able to find one for my filter that way.
The main reason to know the square feet is because that tells you how much DE to use. For example, in my filter, 36 ft wants 4.5 lb, and 60 ft wants 7.5 lb (i.e. 1.25 lb per 10 sq ft). I don't know whether those ratios apply to all DE filters.