Report Abuse. First, know that there are 2.54 centimeters in 1 inch. To convert 20 centimeters to inches, use the conversion factor 20 cm......1 inch --------- * ------------ = 20/2.54 = 7.874015748 inches..............2.54 cm. Son Gokū on the Flying Nimbus · 8 years ago. Thumbs up.2. Thumbs down.irst, know that there are 2.54 centimeters in 1 inch. To convert 20 centimeters to inches, use the conversion factor 20 cm......1 inch --------- * ------------ = 20/2.54 = 7.874015748 inches. .............2.54 cm. Son Gokū on the Flying Nimbus · 8 years ago. Thumbs up. 2. Thumbs down.