SRP76

He can't be far off. He did better against a stronger form of Baby than the likes of Gohan and Vegeta did. Although we don't know exactly what happened to their power between Z and GT, I don't think they got any weaker. They both should have at least been close to Kid Buu's power level.

And Goku's always optimistic; why would he assume Kid Buu was Uub's limit? He could "know that Uub is capable" of a lot more. He's never, ever believed in "limits" to power.

EDIT-

Wait, wait. What were we supposed to be talking about, originally?

Oh, Rildo vs. Kid Buu.

Anyway, Goku claims Rildo is "stronger than Majin Buu". What's the weakest Buu? Mr. Buu. Kid Buu owned him, but not to a "kill you instantly" degree. So, he can't be twice Mr. Buu's power.

Base Goku fought the at least Mr. Buu-level Rildo, and wasn't beaten. To beat Rildo's "true" form, Goku had to multiply his power several times by going Super Saiyan. That would put him way above Kid Buu, and he didn't own Rildo. So Rildo would have to be stronger than Kid Buu.