One way:

Allow: Custom
Formula: =AND(LEN(A1)=4, CODE(UPPER(LEFT(A1,1)))=65,
CODE(UPPER(LEFT(A1,1)))<=90, ISNUMBER(--RIGHT(A1,3)))

In article ,
lhaen wrote:

I want people that use my spreadsheet to HAVE to enter a letter followed by
three numbers. I usually use data validation for tasks like this, however, I
can't figure out have to enforce a custom format of "letter, number, number,
number".