Question: is 16x20 a standard frame size?
Answer: It's a matter of personal preference. 11x14 and 16x20 are standard picture sizes and will give you a nice 2 1/2-3" border which is about right IMO for a 11x14. Typically, the larger the size the larger the mat anywhere from 2 1/2" for 11x14 to 5" or more for a 20x30.