Answer:

“…Do I not fill heaven and earth?” says the LORD (JEREMIAH 23:24).

GENESIS 1:1; NEHEMIAH 9:6; JEREMIAH 10:6; PSALM 86:8

We already touched on this in question one, but let’s look at it a different way. We tend to think of things in terms of a physical size. For example, we can look at how tall people are, how big the dog is, how high the mountains are, how wide the creek is—you get the idea. We compare the things we see when it comes to size. Some things are very big and some things are very small. But God doesn’t have a physical form. Remember? God is spirit and He fills both time and space because He is spirit. We know that God created the universe. (Now that is very big!) And there sure isn’t anything in the whole universe we can compare Him to. 

So, when we talk about how big God is we need to understand that God is infinite. (Infinite means we can’t even measure it and there are no words to describe it—it is forever big). He is infinite in power; that’s big! He is infinite in wisdom; that’s big! He is infinite in knowledge; that’s big! I don’t think we can begin to imagine just how big He is, but it is fun to think about it.

Source: https://answersingenesis.org/kids/creation/how-big-is-god/