"At one of the events, the guys in the back were all testing their strength through arm-wrestling and 'mercy'. Most of them were there to 'impress the divas'. I remember running through all of them, even Paul [Big Show], who had bananas for fingers. The only guy I remember being stronger than me and it pissed me off because I hated not being first, was Kane. No one in the WWE was as strong as that guy. Trying to slam his arm down was like trying to push over a tree with one arm."
But as you probably know, arm wrestling is far from being the ideal test of overall strength.
In another article (Wrestlers Bench Press) Kane was said to bench press several reps with 405 pounds pretty easily.
The guy is huge, despite being billed as 7 feet tall and 326 pounds, Kane is a legit 6ft 7.5in (202 cm) in height. And as any other wrestler his size, he looks like a pretty strong guy.