How to use "tens of" and "hundreds of"?

In English, one would normally say "dozens of" rather than "tens of", so there is some overlap. I might use "dozens of" for an amount between 36 (a dozen, two dozen, dozens...) and 132 (a dozen less than a gross), "scores of" for a number between 40 and 199, and "hundreds of" for values greater than that. I don't think I've ever thought about the reasoning behind this; it would really depend on which number sounded better in the areas which overlap.

As I understand it, the usage is:

Tens of -- rarely used; "as many as XX" might be more appropriate

Hundreds of -- any number from 100 - 999; "more than 500" might be more appropriate for numbers greater than 500

Thousands of -- any number from 1,000 to 9,999

Tens of Thousands of -- any number from 10,000 to 99,999

Hundreds of Thousands of -- any number from 100,000 to 999,999; after 250,000, it is more appropriate to use quarter, half and three-quarter million

I have only heard of "tens" used in, "tens of thousands." Otherwise "scores" is used. Scores being 20-199. And "hundreds" is plural so it would be 200-1999.

When describing victims of a disaster, "tens of" usually means less than a hundred or a bit more, and "hundreds of" can mean up to a thousand or a few more. "Hundreds of dead" could be over a thousand, but the results are still unsure.

"Hundreds of" and "thousands of" are more common than "tens of", but if I heard the statement, I would expect "tens of" to be 30 to about 120 or so. A more common phrase for the same general amount is "dozens of".

You can use hundreds of in sentences like the following.

It costs hundreds of dollars.
An unknown number, probably in the hundreds, had already been lost.
Hundreds of letters poured in.

In the last sentence, hundreds of is used to mean an unspecified large number.

Similarly, you can use tens of (except in sentences like the last one).