Yeah, the only way to tell for sure is to set up your brooder, turn on your bulbs, wait a bit for them to warm up and then check the temperature.
I've used a single 60W red bulb to heat 4 chicks in a cardboard box before and it actually got a bit too warm at times, but that was inside my house. If I had 60 chicks in a bigger brooder in an unheated garage, obviously they'd need a lot more heat to stay at the correct temperature.
P.S. Correct temperature for chicks is usually given as 90-95F for the first week, dropping by 5 degrees for each subsequent week. That's just in the warmest part of the brooder though. Best way to do it is to have a brooder big enough that there are warmer spots and cooler spots, and then the chicks will regulate their own temperature by sitting in the bit of the brooder that's the most comfortable for them. And remember that slightly-too-cold chicks will be temporarily uncomfortable but slightly-too-hot chicks can easily die, so be very careful not to overheat them and always make sure they have access to cooler spots.