[quote=@Kangutso]
<Snipped quote by LokiLeo789>

Catsized!

Also, don't go into the funky smelling one, that's the bathroom.
[/quote]

Technically speaking he can make them as large as he wants as shown when he dropped Grot into the ocean, but the larger the portal the more strenuous it is. I had to spend might to have him make the Grot portal stay open long enough to dunk him.