Weapons scale to character size obviously so you'll want to find a hyur-type character with a Thyrus out. Take as vertical a screenshot as you can so you get a good relationship between character height and the staff.

Break out a stick ruler (or measure in pixels, whatever) and get the height of character/staff ratio, multiply that by your actual height, and you should get the real-life length. Do that with every other important measurement too (like width of the haft, the wings etc.)