I'm confused with the usage of these units, meter, kg
I thought 2kgs, 3meters are wrong ; 2kg, 3meter are correct. However, in an English textbook, I found this sentence, in which it's written, '3800meters'

"The Pacific Ocean is also the earth’s deepest ocean. Its average depth is about 3,800 meters."

Question

I'm confused with the usage of these  units, meter, kg
I thought 2kgs, 3meters are wrong ; 2kg, 3meter are correct. However, in an English textbook, I found this sentence, in which it's written, '3800meters'

"The Pacific Ocean is also the earth’s deepest ocean. Its average depth is about 3,800 meters."

Answer

You're confusing what you do with the SI unit with what you do when you write the word in full. The SI unit for 'kilogram(s)' is 'kg.' The SI unit for 'metre(s)' is 'm.'

It is correct to write 2kg and 3m. Or 3800m. You never make it plural if you use the SI unit.

When you write the word in full, you make it plural (unless of course the number before it is one.)

So two kilograms is correct. As is three metres. And 3800 metres.

Answer

measure units when used with numbers expressing their quantity can be singular or plural, so it's normal if you see it's ending with "s".

meter - meters - m (correct)
kilogram - kilograms - kg (correct)

kgs isn't correct although you may see it somewhere.