To count an interval, count the letter names from the lower note to the upper note, including both ends, to get the number, then count the semitones to get the quality. C to A is six letters, so it is a 6th, and nine semitones, so it is a major 6th.
How do you count intervals?
Counting an interval is a two-step process, and the order matters: count the letters first, then count the semitones. The letters give you the interval number, and the semitones give you the quality. Skip the letter count and you will name the interval wrong, because two intervals can span the same number of semitones but have different numbers: C to F# is an augmented 4th and C to Gb is a diminished 5th, both six semitones, but they are different intervals with different jobs in music. The letter count is simple once you know the musical alphabet, which runs A, B, C, D, E, F, G and then repeats. To count the interval from D to A, count D, E, F, G, A, five letters, so it is a 5th. To count from F to D, count F, G, A, B, C, D, six letters, so it is a 6th. Always include both ends of the count, the starting note and the landing note, and always count in the direction you are measuring, upwards or downwards.
How the semitone count decides the quality
Once you have the number, count the semitones and compare with the standard sizes. For 2nds, 3rds, 6ths and 7ths, the wider version is major and the narrower version is minor: a 3rd of four semitones is major, a 3rd of three semitones is minor. For unisons, 4ths, 5ths and octaves, the standard size is perfect: a 5th of seven semitones is perfect, a 5th of six is diminished, and a 5th of eight is augmented. A handy shortcut is to memorise the major scale: the intervals from the root to each degree of the major scale are all major or perfect, so any note that is one semitone lower than the scale note is minor or diminished. Descending intervals need the same two steps, counted downwards. From A down to F, count A, G, F, three letters, so it is a 3rd, and the gap is four semitones downwards, which is a major 3rd. From C down to A, count C, B, A, three letters, so it is a 3rd, and the gap is three semitones, a minor 3rd. A common trick is to invert the interval instead: a 3rd down is a 6th up, so if you know the 6th up you know the 3rd down. The interval calculator checks your counting, the C major scale shows the major and perfect intervals of a scale, and the key of G major shows the same intervals with one sharp in the key signature.
Worked example — E to C. Count the letters upwards: E, F, G, A, B, C, six letters, so the interval is a 6th. Count the semitones: E to F is one, F to F# is two, F# to G is three, G to G# is four, G# to A is five, A to A# is six, A# to B is seven, B to C is eight, so the gap is eight semitones. A 6th of eight semitones is a minor 6th, because a major 6th spans nine. Check it against the scale shortcut: E major has C# as its 6th degree, so C natural is one semitone lower, which makes it minor. The E major guitar chord uses the major 3rd and perfect 5th above E, both counted the same way.
How to practise counting intervals
Practise counting in short daily drills, away from your instrument first, so the letter counting becomes automatic before you add the sound.
- Write out the musical alphabet starting from a random note, then count the interval to a second random note, letters first and semitones second.
- Count the intervals from C to every white key on the piano, and say whether each one is major, minor or perfect before you check.
- Pick two notes on the guitar, count the interval between them on the fretboard, and check your answer by counting the frets between them.
- Practise descending intervals by counting the letters downwards from the upper note, and check each answer by inverting it to the matching ascending interval.
- Use the interval calculator to quiz yourself on ten random intervals a day, aiming to get the number right every time and the quality right most of the time.
Common mistakes
- Forgetting to include both ends of the count — C to E is three letters, C, D, E, not two. If you count only the steps between the notes, every interval comes out one smaller than it really is.
- Counting semitones before letters — If you count six semitones first, you cannot tell whether the interval is an augmented 4th or a diminished 5th. Letters first, semitones second, every time.
- Using the wrong octave when counting down — When you count an interval downwards, the landing note is below the starting note, not above it. Counting upwards by mistake gives you the inversion, which is a different interval with a different name.
Quick reference
This table shows the counting method applied to six intervals above C, with the letter count, the semitone count and the quality rule side by side. Read each row from left to right and follow the same two steps you would use yourself: count the letters for the number, count the semitones for the quality, and check the result against the rule in the last column.
| Interval | Letters | Semitones | Quality rule |
|---|---|---|---|
| C to E | C, D, E = 3rd | 4 | 3rd of 4 semitones = major |
| C to G | C–G = 5th | 7 | 5th of 7 semitones = perfect |
| C to A | C–A = 6th | 9 | 6th of 9 semitones = major |
| C to B | C–B = 7th | 11 | 7th of 11 semitones = major |
| C to F | C–F = 4th | 5 | 4th of 5 semitones = perfect |
| C to D# | C–D# = 3rd | 3 | 3rd of 3 semitones = minor |
Copy the table by hand with a different root, such as G, and fill in each column yourself before checking your answers: the letters column from the alphabet, the semitones column by counting frets or keys, and the quality column from the rules. Doing it by hand once is worth more than reading the table ten times, because the counting is the skill, not the answers.
Frequently asked questions
How do you count an interval?
Count the letter names from the lower note to the upper note, including both ends, to get the number, then count the semitones to get the quality. C to A is six letters and nine semitones, so it is a major 6th.
What is the fastest way to count intervals?
Memorise the major scale: the intervals from the root to each degree are all major or perfect. Any note one semitone below the scale note is minor or diminished, and any note one semitone above is augmented. That shortcut replaces most semitone counting.
Do I count sharps and flats as separate letters?
No. Sharps and flats modify a letter but do not create a new one: C# is still the letter C, and Eb is still the letter E. The letter count uses the seven letter names only, and the accidental affects the semitone count, not the number.
How do I count an interval downwards?
Count the letters downwards from the upper note to the lower note, including both ends, then count the semitones downwards. Or invert the interval: a 3rd down is a 6th up, a 4th down is a 5th up, and the quality flips from major to minor or stays perfect.
Why does the letter count matter so much?
Because the letter count decides the interval's number, and the number decides its function in chords and scales. C to F# is an augmented 4th, which wants to resolve upwards, while C to Gb is a diminished 5th, which wants to resolve downwards, even though both span six semitones.