Well, you could either divide inches by 2.54 or multiply them by 0.39370079 -unless you would rather purchase a meter stick. If you want to check your work, I'm sure there is a plethora of online conversion tools.
youll have to convert so do the inches really close
dont do just 1/2 inches
do the numbers really really close so you get good numbers after you switch
or try flipping the yardstick over
lots of times theres centimeters on the other side