If you are still learning Hebrew, you might be surprised to learn that the kamatz (the “ah” sound with a little stem in the middle) is sometimes pronounced “oh”. What gives?
What is happening is that there are really TWO kamatzim:
1) The kamatz gadol (“big kamatz”) pronounced “ah” in Modern Hebrew and normally just called “kamatz”;
and
2) The kamatz katan (“little kamatz”) pronounced “oh” in Modern Hebrew.
Unfortunately they are written the same in almost every printed text with a few notable exceptions.
So how do you know how to pronounce it??
The real answer (see below), unfortunately, is quite complicated.
So I will give you three answers, depending on your Hebrew level:
#1: The simple answer: THIS IS THE RIGHT ANSWER FOR 99% OF PEOPLE LEARNING HEBREW!
The simple answer is DON’T WORRY ABOUT IT except for a few common examples. The kamatz katan is quite unusual in Modern Hebrew so just say “ah” in all cases except for כָּל (all/every), חָכְמָה (wisdom), צָהֳרַיִם (noon) and any other case you may come across. If you make a mistake, you will be in good company and the listener will understand you without batting an eye.
In Biblical and ancient Hebrew the kamatz katan is much more common due to slight differences in the language. This is not a big issue for most people unless a) they pray in Hebrew using the common liturgical prayers and b) they use a Hebrew pronunciation which differentiates between the 2 kinds of kamatzim. (Modern Hebrew and some Sephardic pronunciations DO differentiate; most Ashkenazic pronunciations do NOT.) In that case get a siddur (prayerbook) that notes the difference, such as the Rinat Yisrael siddur.
#2: The next step: How to spot a kamatz katan:
Even though answer #1 above is sufficient for 99% of Hebrew learners, and worked for me for decades, I will give you a trick to help you spot a kamatz katan. WithOUT learning the complicated rules.
A bit of background: In Hebrew there are 10 vowels that come in 5 pairs. Modern Hebrew does not differentiate between the 2 vowels in each pair so that simplifies things. So, for example, the regular kamatz and the patach are both pronounced “ah”.
Historically, however, each vowel was pronounced differently and each pair consists of a “big” vowel and its corresponding “little” vowel, which is why there are two vowels in each pair in the first place. There is no difference in meaning between the two vowels of a pair. But each vowel of the pair is used in certain situations based on specific but complicated rules.
The cholom (the little dot vowel that says “oh”) and the kamatz katan are one of the 5 vowel pairs. The cholam is the “big” vowel and the “kamatz katan” is the little one in the pair. That is why it is called the kamatz katan, the “little kamatz”.
Basically a kamatz katan will be used when there should be a cholam but it has been made “smaller”.
So the trick is: If you see a word that you know is pronounced “oh” and/or that usually has a cholam and then you see it with a kamatz instead it is probably a kamatz katan.
To give you a common example already mentioned above:
The word כֹּל in Hebrew means “all” or “every”. For example “everything” is הַכֹּל.
But the word is written כָּל when it precedes another word that it modifies. For example, “all things” is כָּל הַדְּבָרִים. The two words here are a smichut (noun construct); they go together as a pair and that changes around the conditions for how to pronounce the first word in the pair. In this case, therefore, the vowel changes from the cholam in כֹּל to the kamatz katan in כָּל.
#3: The mostly-complete answer — for Hebrew teachers only!
The (mostly) complete answer can be found here:
Wikipedia: Almost everything you could possibly want to know about the Kamatz.
But that is a very technical discussion and assumes you understand other technical concepts related to Hebrew grammar. So I suggest you stick with answers #1 or #2 above.