Say you have a starting note that is written on B. Would you have to fill out all of the sharps that the key of B has to find out the interval?

Like if you had one note on B and the other was on D sharp, would that mean it would be an augmented third, because of the key?

  • 1
    your question seems unclear to me: 1. what instrument do you play? what do you know about chords and intervals? and your example: do you mind a tune or a chord? more information would avoid "wrong" answers, (a. not concerning your question. Commented Oct 26, 2019 at 10:24

7 Answers 7


Yes, the typical approach is to determine the interval based off of the major scale of the bottom pitch.

Given the interval from B up to D♯, we would first conceptualize B major, which has five sharps: F♯, C♯, G♯, D♯, and A♯. Since the D♯ is in the key of B major, this is a major third above B.

In order for this to be an augmented third, we would have to raise this D♯ one half step further to D𝄪 (D doublesharp).

  • Wouldn't B to D# be an augmented third? Because it is an extra half step up. If it was B to D natural that would be a major third right?
    – Jex Pearce
    Commented Oct 25, 2019 at 20:15
  • B to D would not be a major third, because D is not in the major scale of B; only D♯ is. B up to D is only a minor third, since D is in the B-minor scale.
    – Richard
    Commented Oct 25, 2019 at 20:16
  • I understand. Would you have to mark the D sharp in the interval, or would you leave it blank?
    – Jex Pearce
    Commented Oct 25, 2019 at 20:20
  • I'm not sure what you mean. If you're writing a major third above B, you need to clarify D♯. If you're asked to notate the interval from B up to D, this would just be a minor third, and you would not write in a ♯ for the D, because that would change it to a major third.
    – Richard
    Commented Oct 25, 2019 at 20:22
  • Okay, do you also have to think about the E to F being half steps (and B to C) as well with this method?
    – Jex Pearce
    Commented Oct 25, 2019 at 20:23

Just adding notation visuals - otherwise @Richard answered the question.

You must consider both key signatures and accidentals.

enter image description here

With no key signature and no accidentals, B natural and D natural, minor third

enter image description here

With no key signature and accidental sharp on D, B natural and D sharp, major third

enter image description here

With key signature of 5 sharps and no accidentals, B natural and D sharp (from the key signature), major third

enter image description here

With key signature of 5 sharps and accidental double sharp on D, B natural and D double sharp, augmented third (enharmonically a perfect fourth)

Bonus items!

enter image description here

Key signature of two flats and accidental sharp on D, B flat (from the key signature) and D sharp, augmented third (enharmonically a perfect fourth)

enter image description here

Key signature of two flats and no accidentals, B flat (from the key signature) and E flat (from the key signature), perfect fourth

  • Minor third = 3 half steps
  • Major third = 4 half steps
  • Augmented third/perfect fourth = 5 half steps

Notice how the combination of key signatures and accidentals of notation make clear and unambiguous whether two pitches are one of two enharmonic possibilities.


A small addition to address directly the OP's original scenario: a B majro key signature with notes B natural and D sharp notated.

one note on B and the other was on D sharp, would that mean it would be an augmented third, because of the key [B major]?

enter image description here

This is literally what the question posed. The sharp on the D is redundant, because there is already a sharp in the key signature. It's the exact same meaning as...

enter image description here

If the D sharp had been altered, then the sharp could be used to restore it back to the D sharp of the key signature.

enter image description here

If the D was lowered with a natural sign, it will stay D natural until the end of the bar. If you want to set it back to D sharp before the end of the bar, add the sharp.

enter image description here

When the bar with D natural ends, the D is assumed to go back to the key signature as a D sharp. A sharp in parenthesis can be used after a new barline and reminder. This is called a courtesy accidental.

  • Bonus point: In some countries classical players know Bb as B and B as H.
    – ojs
    Commented Oct 27, 2019 at 12:07

Intervals seem to confound many of us. And to make it worse, each pair of notes when played, can be called at least two different names.

The actual key any two notes, therefore the interval between them, can help, but that in itself can bring confusion. Minor intervals are found in major scales, and vice versa.

Intervals are always calculated from the lower note. In your case, it's B. Two factors are needed to establish an interval's name. The first is the letters themselves. Here we count B - C - D. Never mind ♯s and ♭s: just simple letter counting. So, we establish it's a third - of some kind.

Next we address how many semitones are keeping the two notes apart. So counting - B, C, C♯, D, D♯. that's four. 4 semitones makes it a major third.

If you wanted to, you could reason that in key B major, going from B to D♯, you reach the third note in that scale, so yes, it is a major third. But beware, not every interval in a major scale/key will be major. Unless the lower note is root. But even then, P4 and P5 are neither major nor minor! And the same stands for minor. Without getting too deep, D♯ and F♯ are both in B major, but their interval is minor third.


Intervals are absolute. They do not change with different key signatures. B to D♯ is a major 3rd whether the ♯ came from a key signatore or an accidental.

Accidentals are not cumulative. If there's a B major (5 sharps) key signature, a notated D will be D♯. Put a ♯ accidental in front of it (maybe as a reminder after a previous D♮) and it's still just D♯, not D doublesharp.

Yes, a useful way to work out intervals is to consider the major scale rooted on the lower note. If the upper note fits this scale, the interval is major (or perfect if it's a 4th, 5th or octave). Note that it matters whether you call the note D♯ or E♭. B to D♯ will be some kind of a third because there are three letters included in B, C, D. B to E♭ will be some kind of a fourth, because B, C, D, E. You may feel this is an arbitrary distinction! But as you continue your development in reading and analysing music you'll probably see why.


It all depends on the way it's notated, the key is irrelevant (there might not even be a key). If you notate notes as B and D (whether those notes are sharp, natural or flat) then this is always a third. The nature of the interval (major, minor etc.) depend on the number of semitones between the notes.

So we have

  • B-flat to D-flat, B to D, B-sharp to D-sharp ==> minor third
  • B-flat to D, B to D-sharp, B-sharp to D-double-sharp ==> major third
  • B-flat to D-sharp ==> augmented third
  • B-sharp to D ==> diminished third

Or you can take the same interval, notate it in different ways and the name changes:

  • B to D-sharp (or C-flat to E-flat) ==> major third
  • B to E-flat ==> diminished fourth

The written notes in the staff system are not so helpful to understand the intervals (minor, major, diminished or augmented.

You better draw a keyboard and the interval patterns, the note names on the right side of the sheet notation or below of the system.


If you tip on an interval in the posted link the keys and the notations will be shown.

Always keep in mind the bc and ef are half steps (in the staff this is not obvious- but on the keyboard by the structure of white and black keys it is evident: 2 white keys in neighborhood, no black key between them = steps of half tones in the root scale are minor seconds! while all other steps of white keys - with a black key between - them are major seconds.

You have to know by heart where there are minor seconds in the staff system otherwise you won’t be able to develop all the other intervals.

(Then you'll notice that B-D is a minor 3rd and B-D# is a major 3rd. To answer your question: If the starting note is B and the next D# we are probably in B-major and you have to play F#,C#,G#,D#,A#. But a sequence B - D# in the beginning of a tune could also be the upbeat of a song in E-major or e-minor! The latter would only need a F# and probably the augmented 7th and 6th (D#, C#) while E-Major would have 4 sharps: F#,C#,G#,D#.)


Ignore the confusing standard notation, ignore the confusing sharps and flats, ignore the confusing key signatures, and ignore the confusing black/white piano keys. Restrict yourself to only the confusing note names and confusing interval names, and then simply look at the sequence of consecutive notes:

A   B♭  C♭  C   D♭  D   E♭  E   F   G♭  G   A♭  A   
G♯♯ A♯  B   B♯  C♯  C♯♯ D♯  D♯♯ E♯  F♯  F♯♯ G♯  G♯♯ 
0   1   2   3   4   5   6   7   8   9   10  11  12

|                             0 steps — unison, diminished second

        |___|                 1 step — minor second, augmented unison, semitone

        |_______|             2 steps — major second, diminished third, tone

        |___________|         3 steps — minor third, augmented second

        |_______________|     4 steps — major third, diminished fourth

    |___________________|     5 steps — perfect fourth, augmented third

|_______________________…     6 steps — augmented fourth, diminished fifth
|_______________________…     7 steps — perfect fifth, diminished sixth
|_______________________…     8 steps — minor sixth, augmented fifth
|_______________________…     9 steps — major sixth, diminished seventh
|_______________________…    10 steps — minor seventh, augmented sixth
|_______________________…    11 steps — major seventh, diminished octave
|_______________________…    12 steps — perfect octave, augmented seventh
  • Confusing is the right adjective to use! I'm confused by this! OP started at B, not A.
    – Tim
    Commented Oct 26, 2019 at 15:48
  • Why is standard notation, sharps and flats etc. confusing? Been around for hundreds of years and seems to have worked pretty well up to now. Sorry, but I think this is bad advice.
    – JimM
    Commented Oct 27, 2019 at 18:27
  • "Ignore the confusing standard notation..." bad advice. Reading from staff make immediately apparent the basic intervals like third, fourth. The specific quality like major, minor, diminished, or augmented then come from the key signature and accidentals. Commented Oct 28, 2019 at 12:40
  • @MichaelCurtis, that after seeing the obvious part one then has to look at the key signature and figure it out just illustrates how overly complex standard music notation is. I'm not suggesting that this notation will ever be redesigned to be based on 12-semitones rather than on the current black/white piano keyboard. But when learning, until one is very familiar with the standard notation it is a lot easier to work out and understand what is actually going on if one discards the additional complexity. Commented Oct 28, 2019 at 13:24
  • "...until one is very familiar with the standard notation..." if you don't learn the keys and don't learn notation, of course it will be confusing. I think the better advice it: learn to read. Commented Oct 28, 2019 at 16:33

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