Well there's not a definitive answer because ... "a slice of regular pizza" is a pretty random item. I mean, first of all, what's "regular"? Is it one slice from a large pizza with pepperoni and extra cheese? Is it one slice from a medium veggie-lovers pizza? Is it one slice from a large meat lover's pizza? Is it homemade? From Pizza Hut? From Dominos? From Papa John's?
See, there's no such thing as "regular" pizza.
You can check out some of the calorie counting sites and even some of the chain stores to get some calorie estimates.
For example, Pizza Hut has nutrition information on their website here:
It'll tell you that 1 slice of a medium, hand tossed, supreme pizza is 260 calories. 1 slice of a medium, deep dish, meat lovers pizza is 330 calories. 1 slice of a large, deep dish, meat lovers pizza is 470 calories. Etc.
As you can see, "regular" doesn't really mean anything.