First, convert your feet and inches measurement into just inches. Do this by multiplying the number of feet by 12 and adding on the number of spare inches. Then, multiply this value by 2.54 to get the result in centimeters.
For example, if you are 5 feet 8 inches tall: 5 x 12 = 60, 60 + 8 = 68, and 68 x 2.54 = 172.72 centimeters.
You multiply by 12 because that is how many inches there are in 1 foot and by 2.54 since it is the number of centimeters in 1 inch. Alternatively to this, you could use an online converter tool to ensure you don't make any mistakes. However, in case you don't have an Internet connection at the time, it is useful to remember this method.