Writing. Triond. GlobalVoices Summit 08. The Griffin Outpost. 12 Point Font-Size Line Length Rules of Thumb: 'Points-times-two': 12 point * 2 = 24 picas = 384 pixels 'Alphabet-and-a-half' (39 characters): 12 point = 15 pixels per char = 311px total Average of both: 347 pixels Leading for 12 Point Font-Size: The 120% rule: 15 pixels per char * 120% = 19 pixels.