I understand how to work out intervals, bottom note to top, think in the major key. But what if the bottom note is G Sharp?

Well the way I do it is ignore all the sharps and flats until the end:

Say you have G# to B as an interval.
Ignore the signs, lok at just the letter names G to B. So it is a third of some kind.
Now think of G major. In G major, a G to B would be a major third.
This interval is a semitone less than that because the G is sharpened.
So it must be a minor third.

I know everybody has different ways of doing intervals, but that's always the way I found easiest - use the 'bare' letter names to find out the quantity and then worry about the flats/sharps for the quality.

You could do the same for G# to Bb.
It's still G to B, so still a third of some sort.
G to B is your major third...this one is two semitones less because of the sharp G and the flat B...so it's a diminished third.

Then there's Gb and B, Gb and B#, and all sorts of weird things you can do. I think I found sticking to one pair of letter names when I started working these out was the way I found it easiest, so for example looking at all the possible combinations of Gs and Bs.

Technically, you can work it out in the same way going up the major scale where in this case every note is a sharp an F is double sharp: G#, A#, B#, C#, D#, E#, Fx, G#. If you have G# at the bottom and say B# above, it is a major 3rd or if the top note is B, then it would be a minor 3rd.

The G# major scale is the enharmonic equivalent of Ab major - it might help you visualise it or hear it in your head more clearly but it probably doesn't help to think about Ab major instead. You could think of the bottom note as G and work out the interval and then adjust it by the semitone to take into account that the bottom note is actually G# rather than G.

Hope this is useful and not more confusing!

Yes I would take the same view , and think of it as A flat scale

Thanks very much. Will try these solutions to see which works best for me.

My method for odd lower notes, is to adjust both notes by a semitone so that you get something more user-friendly

For your example - G sharp to B, I would lower both notes by a semitone - now you have G and B flat - much easier to work out, and it gives you the same answer (note that the numerical value of the interval is not altered).

I would avoid enharmonic equivalents - thinking about A flat instead of G sharp could lead you to conclude that the interval is an augmented 2nd. Fine if you are working out how to pitch a note, but not so good for interval theory!

I am with Louise H on this.

... and I'm with SueHM. I agree with her about enharmonic stuff - vastly useful but can be confusing with intervals unless you really understand which bits work and which bits don't in this context.

I'm with Maizie, SueHM and maggiemay on this. I'm afraid I can't see how using the enharmonic names will help at all - perhaps F#minor and Mad Tom could elaborate on why they say this is a good way of doing it - I'm always open to discovering new ways of working out intervals - anything to help the kids get the answer

Whoops. I DON'T think using enharmonic equivalents is wise. It is LouiseH's first paragraph that I was agreeing with - that and where she says "it probably doesn't help to think of Ab major"

If "Getting the right answer" is the aim then do whatever is convenient.

If understanding music is the aim then:

1. It is fundamentally simpler to work out intervals in the actual key. Imagining it is in some other key (even an enharmonic one), working it out, and transposing back, adds two unnecessary steps. Keys like G# are only more difficult because of unfamiliarity, not because of any conceptual difference. So it is a good idea to take the opportunity of geting used to keys that contain notes like B# and F##.

2. In a piece of music (even keyboard music), where there is a transposition the composer will write in the key that indicates the harmonic function/relationship of the new key, rather than use an enharmonic equivalent that is superficially eaasier to read [e.g. some of ALbeniz's modulations in the pieces of Iberia]

3. The notes Ab and G# are not the same except on a keyboard instrument.

I don't mind SueHM's method. I agree strongly with her and maggiemay's warning not to think about enharmonic equivalents: they are a snare and a delusion when you are working out intervals.
... and not all of them. Harpsichords and organs with split keys to distinguish sharps from nearby flats have survived (from the 17th C IIRC).

Intervals always seem to cause trouble. I've only ever had one student who seemed to just 'get it' in one go, but then he is a highly unusual chap with a very analytical mind, who swallows chunks of music theory whole. Everyone else seems to get a bit strung up and need several sessions on intervals. If you need more practice at identifying and checking your answers, you could try this excellent website - sometimes knowing the answer and working backwards is helpful. The vast majority of students will never need or want to go beyond grade 5 theory, so don't let the thought of B sharp major give you nightmares!