How big is the universe in km?
It's quite big
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.