1 yardstick is equal to 1 yard, which is also equal to 3 feet. If you line the end of the yardstick up with the end of the rug, you can figure out 3 feet in. Then line the yardstick up at the 3 foot mark to determine where 6 feet is. Keep laying the yardstick across the rug until you have an overall estimate of how many feet you have. Add up the number of times you have laid the yardstick down and multiply by 3 feet.
Hope this helps! :)