Utilize Field Length As An Affordance

The length of the field affords the length of the answer. Employ this for fields that have a defined character count like phone numbers, zip codes, etc.

Text fields should be about the same size as the expected input since it’s extremely error prone when users can’t see their full entry. For example, for 2,130 recent participants in the UX Conference, the user’s city of residence ranged between 3 characters (Leo, Indiana) to 22 characters (San Pedro Garza Garcia, Mexico). 99.9% of city names were 19 characters or shorter, making 19 characters a reasonable width for a city field.