What is the common expression to describe position starting from the last one?

Suppose we have letters: a, b, c, d, e, f ,g.

I want to describe the position of letter "e" starting from right hand side, what should I use?

"e" is the last third letter.

"e" is the third last letter.

"e" is the last but two letters.

Which one is commonly used? Or other ways to describe it?

Thanks!

Solution 1:

Typically you'd expect to hear:

"e" is the third from last letter

or

"e" is the third to last letter

and you may sometimes hear

"e" is the last but two

Solution 2:

The common usage would be "third to last". If you need a weird word, use antepenultimate or propenultimate:

"Two before the last, i.e., the one immediately before the penultimate, in a series."

This book has ten chapters — chapter 8 is the antepenultimate one.

(From Wiktionary)

Solution 3:

Antepenultimate means before the next to last.