I took the opposite approach.<p>I checked all the boxes on the first page but one, "vibrissae" (roughly, whiskers), and saw even more boxes on the second page and groaned. So I punted, and went back to the first page, reloaded it, and checked only one box: vibrissae.<p>After finding 17 words on the second page, I left them all blank, following the same methodology. My vocabulary size was estimated to be 20 words.<p>From this, I deduced that my total vocabulary size was all the words ever known to any English speaker anywhere, anytime - minus 20.<p>This made me very pleased with myself, even though I knew my assumptions were pretty terrible.<p>(Interesting that the spell check in my browser doesn't recognize vibrissae.)