How can you tell what key a song is in by listening to it?

[Knight Vista]

I've tried looking it up but all I find is how to tune your guitar tutorials.

Any help?

[vampiresrock]

Learn the notes of the melody by ear and whatever key they're in is the song's most likely key? Alternatively the first and last chords of a song sometimes indicate the tonic of the key in a lot of pop so figuring both out would help.

[Zillamatic]

Play along on your instrument of choice, and you should know what chord/root notes you're playing

[Katamari101]

You can figure it out by playing the song in your instrument of choice, but figuring out the key just by listening requires a really good (or perfect) sense of pitch.

[killerteacup]

if you don't have perfect pitch then its a hard knock life

alternatively when using an instrument -

Check out the note the song ends on - if the song sounds like its been completely resolved, then its the tonic and if it sounds like its been cut abruptly short, it aint the tonic

Play along, identify chords

Jam along to the song using an aeolian mode until you find that all the notes fit and thats the relative minor

[charozoid]

Once you get pretty good with chord progressions, you can pretty much say what progression is in the song, then you just need to find the key.