synonyms - 量、数 and 数量 (amount). Is there any of them that is used far more frequently than the other ones or are they pretty much equally used?

Assuming all of the three words are used to convey the same meaning, is there any of them that is used far more frequently or on the other hand they are equally used but differ depending on the context, etc?

I learnt the word 量 (りょう) some time ago as "amount". However, I recently came across the word 数 (すう) conveying "amount" as well. I looked up both words in Jisho and their meaning appears to be the same according to the definitions "quantity; amount​". I noticed that in the case of 数, the primary usage seems to be as a prefix rather than a plain noun. To make it even more complicated, there also exists the word 数量 (すうりょう) that makes use of both characters and according to Jisho it means "quantity; volume; amount". I researched a bit around the internet for an explanation on these words with no luck.

Thank you very much.

Answer

These are all used to describe or measure quantity. The difference is whether what is being measured is countable or not.

量 - How to show amount (weight, volume, proportion). Used for uncountable items.

数 - How to show number. Used for countable items.

数量 - A general way of saying quantity or quality (or both) without having to be specific about which.

分量 - How to show the measure of a fixed non-countable quantity.

個数 - How to show the measure of a fixed countable quantity.

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When describing how much food is on one's plate in plain terms, one would use 量, while the number of sausages on one's plate would be 数. [A lot of food vs. Many sausages]

When determining set serving sizes/quantities: For mashed potatoes one would use 分量, while number of sausages would be 個数. [Amount of mashed potatoes to be served vs. Number of sausages to be served]

When describing the serving sizes/quantities in general (without being specific), one would use 数量. [Amount and number]
Also, when ordering online, often the field for quantity/number to be ordered uses the default 数量, as it would be too much trouble to tailor each field to each individual product.

In colloquial terms, 量{りょう} and 数{かず} are the most commonly used.