The distance between any two notes — and why it matters
Start with your ears, not the words. Press these, then read on — one feels close, one feels wide.
What you’ll learn in this section
- What an interval is — a fixed distance between notes that keeps its identity wherever it sits on the keyboard
- Naming intervals by size (2nd, 3rd, 4th…) and quality (major, minor, perfect)
- How thirds build chords — and why a single semitone makes the difference between major and minor
A distance that travels
An interval is the distance between any two notes, measured by how many semitones separate them. The key insight — and it is a beautiful one — is that the interval is an abstract distance, not a fixed pair of notes.
Think of it as an elastic band stretched to a certain length. Move the whole band up or down the keyboard: the notes change, the letter names change, but the length stays the same and the sound of the distance stays the same. A major third sounds like a major third wherever it lands.
This is why musicians name intervals rather than just naming note pairs. “The note four semitones above this one” is always a major third — in C major, in F major, in any key.
A major third on the keyboard
Here is C to E: four semitones apart (C to C♯, C♯ to D, D to D♯, D♯ to E). The teal keys show the two notes; the bracket above shows the span. Move that same four-semitone gap to start on D: D to F♯ — still a major third, different notes, same sound.
Same distance — 4 semitones — on different notes, yet the same major-3rd sound.
The bracket spans C to E: 4 semitones, skipping two black keys. Any 4-semitone gap is a major third.
Two parts to every name
An interval name has two parts: a number and a quality.
The number counts how many letter-names the interval spans, including both ends. C to E spans C, D, E — three letter-names — so the number is a third. C to G spans C, D, E, F, G — five — so the number is a fifth. Always count the note you start on as “1”.
The quality refines the exact number of semitones:
- Perfect — for unisons, 4ths, 5ths and octaves: only one standard size each
- Major — the larger version of a 2nd, 3rd, 6th or 7th
- Minor — one semitone smaller than major (for 2nds, 3rds, 6ths, 7ths)
The intervals from C
| Interval | Semitones | Example (from C) |
|---|---|---|
| Perfect unison | 0 | C → C |
| Minor 2nd | 1 | C → D♭ |
| Major 2nd | 2 | C → D |
| Minor 3rd | 3 | C → E♭ |
| Major 3rd | 4 | C → E |
| Perfect 4th | 5 | C → F |
| Perfect 5th | 7 | C → G |
| Minor 6th | 8 | C → A♭ |
| Major 6th | 9 | C → A |
| Minor 7th | 10 | C → B♭ |
| Major 7th | 11 | C → B |
| Perfect octave | 12 | C → C (higher) |
Minor and major 3rds are highlighted — you will use them constantly when building chords in the next section.
Sweep every interval from C
Use − and + to set the distance, then Name it to hear the two notes and see what the interval is called. Work up from a semitone to the octave and let your ear attach a name to each width.
The third: the building block of chords
When you stack a major third (4 semitones) and then another interval on top, you get a chord. The next section shows this in detail, but the key preview is this: whether a chord sounds major (bright) or minor (darker) depends entirely on whether the lower interval in that stack is a major third or a minor third.
In other words, one semitone — the difference between a major and a minor third — changes the entire character of the chord. Intervals are not abstract: they are the architecture inside every sound you play.
Train your ear
You met the major and minor third by sight — now catch them by ear. Play the two notes, then choose.
Press the buttons below to hear C and E (major 3rd: 4 semitones). Now move E down one key to E♭ (minor 3rd: 3 semitones). That shift from brightness to shadow is the semitone of difference between major and minor.
One semitone in the middle flips bright to shadowed.
Major triad = major 3rd (4st) + minor 3rd (3st). Minor triad = minor 3rd (3st) + major 3rd (4st). One semitone changes the character entirely.
Check your understanding
How many semitones is a major third?
C up to G is a perfect what?
What quality does a 3rd, 6th or 7th have when it is one semitone smaller than major?
Drag the interval band along the keyboard, hear every interval in context, and test yourself identifying intervals by ear.
Hear two notes and name the interval, scored with a running streak. Each one comes with a famous-song hook to lock it into your ear.