Our rulers are free for personal use. What this means is that you can use them for free for your personal projects without asking for permission, but you cannot distribute them (upload them on any other site or reproduce them in any other medium) or sell them.
Hold a blank paper against your ruler as shown on the image. Letter sized paper should measure 27,94 centimeters or 11 inch vertically. A4 sized paper should measure 29,7 centimeters or 11,6 inch vertically.
BTW, be careful with your spelling: in case you didn't know, ruller with double-L is incorrect :)