You asked for it. Here's the 1st generic thread for the FAQ sticky thread. This one gets asked a lot and we all have our different opinions. So post yours. Include answers for different gig sizes, types of music, etc. Feel free to post links to any of your favorite threads where this topic has been addressed as well. i merged this thread with an old one i did - below is my original post and the original reply by sundouge. There are many situations where a player can get away with using a small 100 watt combo or what have you. I'm not really adressing these type of situations, rather I'm coming from the perspective of advising someone who can only have one rig and wants enough flexibility volume wise to be able to play medium sized gigs, play with moderately loud guitar players and drummers, etc, and who doesn't want to find out in a year that what was fine for practice won't cut it in the gigging world. There are two factors to consider, watts and speaker configuration. As far as watts go I feel that you should have an amp that will put out at least 200 watts into the speakers you are using, and that 400 watts is much closer to optimum. Before choosing an amp you should determine what speakers you are going to use and what the total impedance of the cabinet(s) will be so you can make sure you'll be actually using 200 - 400 watts at that impedence. In terms of minimum speaker requirements i think a single 12", two 10" drivers, or a single 15" speaker is the bare minimum. I'm also in favor of having a two 8 ohm cabinets instead of one 4 ohm one if you can manage it. A 4 ohm 4x10 or 2x12 is actually great, but i'm not a huge fan of 4 ohm 2x10 cabs. (ditto for 4 ohm 1x12 or 1x15 cabs). All things being equal a 4 ohm 2x10 will be only slightly louder than an 8 ohm 2x10 on the same amp. You're better off saving your money and getting a second 2x10, 1x12 or 1x15 in the future which will give you more volume due to the additional speaker area.