You can learn about tennis stringing using this application contains instruction text and video. And you can calculate necessary string length in one piece stringing or two piece stringing considering racket face size, string pattern (i.e. 16x19, 18x19) . Calculated length is converted number of racket length, You can find quickly string length for various racket.
Sorry, instruction material (text and video) are written by Japanese, not English. But Calculator support English.