Give your students Nation's Vocabulary Levels Test (mentioned on the page above).
Then analyze a text or text sample using Paul Nation's Range software or VocabProfile program on Tom Cobb's website.
Paul Nation's Range software is useful for marking the words in a text according to which list they appear on.
The marked text which the Range software produces can be reformatted in Word using my VocabMark macro.
To install the macro, click on the VocabMark link. Copy the entire text. Open Microsoft Word and press Alt + F8 to open macros. [Alternately, you can select the "tools" menu / "macros" / "macro..."] Click on "step into" to open the macro file in the Visual Basic editor. Go to the end of the file and paste the VocabMark macro into the file. Save the file and close it.
To reformat your marked text, use MS-Word to open a "marked" file produced by Nation's Range34 software. Press Alt + F8 and select "VocabMark" from the list. Press "Run" and your text will be reformatted using regular, bold, underlined and italic print.
To calculate how many of the words in a text your students will probably know. Download the Vocabulary Coverage spreadsheet and fill in the data from the Levels Test and text vocabulary profile.