I Go By Dpi (400) And Pxs (1200x1600) - Tumblr Posts

i go by dpi (400) and pxs (1200x1600) your telling me this is equal to 3 fuckin inches?? someone explain the logic aksjfgaskjfgsakjgha there must be some conversion that makes sense because i had plenty of drawing area i was sure this was equal to 8x10 EXPLAIN SDJKSAJGH'ASL