How do I find out what key a musical composition is in?

Question

I'm trying to figure out what key a song I've composed is in (I have a bad musical ear), and also Iron Maiden's Hallowed be Thy Name

Answer 1

Think about what chord you are playing the most. That would usually be the "tonic chord" and the lowest note of that chord is the name of the key. If you know the name of that chord, that is the name of the key as well. If you don't know the name, but can hear the same note played on a guitar and piano, then match that note to a key to figure out what the name of the note is. The white key before a group of two black keys is called C. The white keys are in order c,d,e,f,g,a,b, and then you should be at c again. The balck notes are the same letters plus sharp if the note is higher than the white key ex. c sharp or flat if the balck note is lower than the white key- d flat. b and c and e and f are next to each other without a black note betwen them. This pattern of balck and white notes on the piano keyboard repeats many times- each repeat is called an octave.

Answer 2

Write down your flats or sharps in order...
sharps:fcgdaeb
flats: beadgcf

if it's sharps, then you go to the last sharp and go up a half a step (like if you were on a keyboard, and your last sharp was b sharp, then your key is c sharp major)

and if it's flats, then the second to last flat is your key (last flat is d, then it's a flat major)