Yeh heat pads come in different sizes as well as brands.. All depends on how big of a tank you got, you want about 1/3 of the tank warmed by the heating pad if your using a smaller cage.. for 1 of my mansions i can only cover a small portion tho with a huge pad. ,lol..
Couple alternatives.. You can buy a human heating pad at a drug store, walmart, places like that an use instead of 1 specifically for reptiles.. They are cheaper sometimes and you can control the strength it is putting out by using the Hi,Mid,Low feature if its too warm for your cage..