Question

How big is the universe in km?

Answer 1

It's quite big

Explanation:

The universe in light years is about 46 BILLION LIGHT YEARS, so that's a lot.
And even 1 light year is equal to 9.461e+12, so that even can't be counted, and 46 billion light years is equal to 4.35193601739e+23, so it can't be sort of counted.
Hope you understood.

Answer 2

The diameter of the observable universe is about `4.40` x `10^23` km.

Explanation:

The diameter of the Observable Universe is about 46.5 billion light years or `4.40` x `10^23` km.

Source:
Observable Universe