Amazingly, one of the most basic concepts of music theory doesn’t seem so basic: key signatures. I am constantly running into people who either a) don’t know how to tell what key they’re in or b) know what key they’re in but consistently forgot to add the sharps and flats in the key signature. Before we look at the steps to figuring out how to find the key signatures, let’s realize that the absolute best way to know what key you’re playing in is to memorize what every key signature is so that you can tell at a glance what key your in AND get comfortable playing in all of those keys so that you won’t miss the notes in the signature. Visit musictheory.net for some helpful practice on key signatures.
Step one: figuring out the key.
There are several ways to figure out what key you’re playing in. The most basic way is to look at the first and last note of the song and determine from that. If the song starts on an E and ends on an E, there’s a pretty good chance that you’re playing in the key of E. That’s not the case all the time, however, so let’s figure out the no-mistake ways to find your key.
Sharp keys (keys with sharps in them):
Find the last sharp in the key signature and go up a half step. That’s the major key your playing in. It’s that simple. The key of D has F# and C# in the key signature. Going up a half step from C# brings you to D.
Here’s the catch, though: remember the relative minor chord we talked about in tip #4? It’s possible that you might be in that key instead of the major key. A few ways to tell are to look at the first and last note or chords in the song. You can also play the song and listen to whether or not it sounds more joyful or more somber. If it’s more somber, you’re in a minor key. So to find the minor key, first find the major key, then go down 3 half steps (minor 3rd) to the relative minor and there you have it. As I mentioned earlier though, it is much more effective to memorize all key signatures and relative minor keys of each major key so that you instantly know that D major and B minor have the same key signature.
Flat keys (keys with flats in them):
Find the second to last flat in the key signature. That’s your key. In the key of Eb the signature is Bb, Eb, Ab. The second to last flat is Eb, thus your key. The one exception to this is the key of F, which only has one flat. We can also find flat keys by going down a perfect 4th (5 half steps) from the last flat in the key. So, since Bb is the only flat in the key of F, and the last flat, going down a perfect 4th brings you to F. The same applies for the relative minor for flat keys. Once you’ve found the major key, go down a minor 3rd (3 half steps) to find the relative minor key.
Memorize the Key Signatures
Again, it is much better to figure out every key signature and memorize them so that you can know them in an instant. The more you familiarize yourself with how key signatures look, the quicker you’ll be able to tell what key you’re in. The more you familiarize yourself with how keys feel as you play them, the more comfortable you’ll be playing in those keys.