Now we have some visuals we can to compare the hole to better estimate the size. We can all see it is nowhere near as big as some claimed it was last week.
Here is Big Mom falling in the hole.
We can see the hole is bigget than Big Mom but not gigantic compared to her.
Here is Kaido and Big Mom on the skull dome.
We can see those two are the tiny specks on the dome. We can't even see the complete dome in the scene. By comparing that scene to the hole Law created it can easily be determined the hole is not bigger than the dome and if it's not bigger than the dome it's not bigger than the island.
Here we can see Zoro is a tiny speck compared to the golem's waist.
Big mom is bigger than Zoro but she's about 5 times taller than him. Big Mom will not be bigger than the golem waist.
Luffy and Zoro has similar height.
From all of those facts we can see the hole that Law created would be no bigger Pica golem waist.