Take the test and mark all the words you know. Do not check those you know you've seen somewhere, but don't know their meaning now. Also you may encounter an easy word like weasel, but if you don't know whether it's lasička or kuna, then don't mark it. After you've taken the test, you're going to get an estimate on how many words you know. It's pretty much faster than going through the whole dictionary of yours. Quick and quick-ly don't count as seperate words, but it also doesn't count all the idioms you know etc. If you don't know a certain word, then look it up, but don't check it afterwards.
My score is: 12800 words (But, remember it's only an estimation of my vocabulary, so I would tell between 11k and 13k is about right.) Now it's your turn and please do not cheat, cause where's the fun in it? I've personally taken the test several times to make an average of my vocab. Good luck
Most Native English adult speakers who have taken the test fall in the range 20,000–35,000 words. And for foreign learners of English, we've found that the most common vocabulary size is from 2,500–9,000 words