At present the No Boundary Condition is accepted for the Universe.
We imagine the Universe just like the Earth.
You start at one point, go all the way round and come back to where you started.
The Universe is also similar. So, we don't know the exact length of the Universe
However, most probably, it's not infinite


Nobody knows if it is infinite or no
 maybe it is very big that the scientists still didn't find how huge it is!
But if it is infinite nobody knows the reason  
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We really do not know if the universe is infinite at this point,but since the value is so close to flat,even the universe is positively curved and finite,it would be definitely much much bigger than the observable universe.
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