How many watts do i need to power my 500 watts MTX ThunderPro subwoofer?

look at the RMS rating on the sub woofer.and how many ohms it is.what you need is a class d or mono amplifier that is a match for RMS to what the sub woofer can handle.never use peak or max power ratings to match up a sub woofer to an amplifier.you also can use a bridgeable channeled amplifier on lp or low pass and matching it to your sub works the same way,look for the RMS rating the amplifier is putting out in a bridged mode.and remember a match is what your looking for at whatever ohms load the sub woofer is.most subs are 4 ohms but not all,some are 2 ohms.this all is important when it comes to wiring the sub up.go to (www.rockford fosgate.com woofer wiring wizard),and use there chart to wire your subs to an ohms load it can handle.the RMS rating is the normal or continuous power a class d amplifier can put out and a sub woofer can handle.a channeled amplifier will give you these figures in a bridged mode or per channel so you can match up speakers to each channel for mid's and highs.using that chart is very important when wiring your sub up.and you can use (www.youtube.com/car audio) then sub woofer in stallion or whatever your interested in.they have many how to videos on youtube and can be a great help when your installing this equipment.no matter how many sub woofers your going to have you have to add the RMS ratings of all together and match this figure to a class d amplifier.this is why this chart i told you about is important,take a look at it.its all in the wiring as to what ohms load you end up with.total watts is not how you match any sub woofer or speaker to an external amplifier,the RMS the normal or continuous power is.good luck with your sub woofer.and it could be a dual coil sub woofer,you can tell if it has 2 sets of contacts for power and ground,this is why this chart is so important.and the size of the en closer also matters.google the type sub woofer you have and you can download the owners manuel.