Column validation on a non required field

Question

I would like to have validation on a column that IF you type in the field you have to use 19 letters. But if you leave the field blank you can still save.

Right now I use this:

=IF(LEN([column 1])=19

Answer 1

Try using below formula:

=IF(ISBLANK([column 1]), true, IF(LEN([column 1])=19, true, false)

This will allow users to add either blank values or the text with length of exact 19 characters.