An hour is correct because the “h” at the beginning is silent so hour is pronounced with a vowel sound. Vowel sounds use the “an”.
What is the rule for a and an?
We use ‘a’ before words that begin with consonants(b, c, d, g, t, y) and we use ‘an’ before words that begin with the five vowels(a, e, i, o, u).
This rule does not apply to how the word is written. It applies to how the word sounds.
The ”h” at the beginning of “hour” is not pronounced so “hour” sounds like “our”. For that reason, we need to use” an” and not “a”.
What about the word “hotel”?
Well, in this case, we pronounce the “h” so it is “a hotel”
Let’s look at other examples beginning with H
He is a human.
You have a heart of gold.
We have a history together.
We need a hinge for the door.
It would be an honor to attend your play.
Your son is an honest boy.
Is it “a herb” or an “herb”?
Herb is pronounced with a silent h in American English but the “h” is pronounced in British English.
Can we add an herb of some kind to the dish? (American)
Can we add a herb of some kind to the dish? (British)