A perfect fourth spans four letter names and five semitones. C to F is a perfect fourth: C–D–E–F gives the four-letter span, and the pitches are five semitones apart.
The abbreviation is P4. You’ll hear it in melodies, suspended chords, guitar tuning, bass lines, and chord voicings. Learning its structure also makes musical intervals easier to identify.
What Is a Perfect Fourth Interval?
A perfect fourth is a diatonic interval whose notes are four letter names apart and whose pitches are separated by five semitones. For example, D to G is a perfect fourth because D–E–F–G spans four letter names and the two notes are five half steps apart.
The word “fourth” describes the letter-name span, not the number of semitones. Count both notes:
D (1) – E (2) – F (3) – G (4)
The number tells you the letter-name span, while the quality—perfect, major, minor, augmented, or diminished—describes the exact size.
Why is it called “perfect”?
The perfect fourth belongs to the perfect interval family with the unison, perfect fifth, and octave. These intervals are not labeled major or minor in standard tonal theory. Their basic form is called perfect; raising it by one semitone makes it augmented, and lowering it by one semitone makes it diminished.
“Perfect” does not mean that the interval sounds better than others. A justly tuned perfect fourth has a 4:3 frequency ratio: the upper note vibrates four times for every three vibrations of the lower note.
How Do You Build a Perfect Fourth?
To build a perfect fourth above any note, count four letter names from the starting note, then adjust the accidental so the two pitches are exactly five semitones apart. Both checks are necessary because semitone distance alone does not determine correct interval spelling.
Step 1: Count four letter names
Suppose you want a perfect fourth above A. Count A as the first note:
A (1) – B (2) – C (3) – D (4)
The upper note must therefore use the letter D.
Step 2: Confirm five semitones
Now count the half steps from A to D:
A–A♯ (1), A♯–B (2), B–C (3), C–C♯ (4), C♯–D (5)
A to D is five semitones, so it is a perfect fourth. A chromatic scale guide can help when you’re still learning to count half steps.
Perfect fourth reference table
| Starting note | Perfect fourth above | Semitones |
|---|---|---|
| C | F | 5 |
| D | G | 5 |
| E | A | 5 |
| F | B♭ | 5 |
| G | C | 5 |
| A | D | 5 |
| B | E | 5 |
F to B♭ is the example most likely to trip up beginners. F to B spans four letter names, but it contains six semitones and is therefore an augmented fourth, also called a tritone. Lowering B to B♭ produces the required five-semitone distance.
Correct spelling preserves musical function. C to F is a perfect fourth, while C to E♯ is an augmented third even though E♯ and F sound alike on an equal-tempered instrument. If spelling is unfamiliar, review how musical note names work.
What Does a Perfect Fourth Sound Like?
A perfect fourth sounds open, stable, and slightly unresolved depending on its melodic or harmonic context. In 12-tone equal temperament it measures 500 cents; in just intonation, the 4:3 ratio produces approximately 498 cents.
“Amazing Grace” begins with an ascending perfect fourth. Use melodies as memory aids, but train from several notes so you learn the interval rather than one song’s pitches.
How to recognize it by ear
Use this short routine:
- Play a starting note and sing the opening leap of “Amazing Grace.”
- Check whether the sung note is five semitones above the starting pitch.
- Repeat from several notes in comfortable parts of your range.
- Practice the notes together as well as separately.
- Reverse the notes to learn the descending form.
Melodic recognition means hearing the notes one after another; harmonic recognition means hearing them simultaneously. A structured interval ear-training routine should include both forms.
Song associations help at first, but relative-pitch practice is more flexible. Sing a P4 from a random note, check it on an instrument, and correct it immediately. These ear-training exercises develop that process.
How Is a Perfect Fourth Used in Music?
Perfect fourths appear in melody, harmony, instrument tuning, and chord voicing. Their effect ranges from spacious and stable to suspended and tense, depending on the bass note and surrounding harmony.
Melodies and suspended chords
Melodic fourths create a clear leap without sounding as wide as a fifth or octave. Composers and songwriters use them for memorable openings, energetic bass movement, and call-like phrases.
In harmony, the fourth often appears in a suspended-fourth chord, written sus4. A Csus4 chord contains C–F–G: the usual third, E, is replaced by F. The F commonly resolves downward to E, turning Csus4 into C major. The sense of tension comes from harmonic context, not from the fourth being inherently harsh.
Guitar tuning and instrument layouts
Standard guitar tuning is mostly organized in perfect fourths: E–A, A–D, D–G, and B–E are all P4 intervals. The G–B pair is a major third, which breaks the otherwise regular pattern. Understanding that layout supports practical skills such as tuning a guitar by ear.
On a standard-tuned guitar, the same fret on most adjacent string pairs produces a perfect fourth, except between G and B.
Is a Perfect Fourth Consonant or Dissonant?
A perfect fourth can be consonant or dissonant depending on context. It is generally treated as consonant in melodies and between upper voices, but traditional tonal counterpoint often treats a fourth above the bass as a dissonance that requires preparation and resolution.
For example, F above a bass note C forms a perfect fourth. In a suspended texture, F may resolve to E, creating a third above the bass. However, the same notes F and C can sound highly stable when F is the bass because F to C is then a perfect fifth.
This explains why blanket statements such as “the perfect fourth is always consonant” or “the perfect fourth is always dissonant” are misleading. Register, bass position, style, voicing, and resolution all affect how listeners perceive the interval.
Perfect Fourth vs. Major Third, Tritone, and Perfect Fifth
A perfect fourth is larger than a major third, one semitone smaller than a tritone, and two semitones smaller than a perfect fifth. Its most important relationship is with the perfect fifth: the two intervals are inversions of each other.
| Interval | Abbreviation | Semitones | Example above C | Characteristic |
| Major third | M3 | 4 | C–E | Defines a major triad |
| Perfect fourth | P4 | 5 | C–F | Open or suspended |
| Augmented fourth / tritone | A4 | 6 | C–F♯ | Unstable, tense |
| Perfect fifth | P5 | 7 | C–G | Open, stable |
Inverting an interval means moving its lower note above the upper note, or vice versa. C up to F is a perfect fourth; moving C above F creates F up to C, a perfect fifth. The interval numbers add to nine, and the two semitone counts add to twelve.
The perfect fifth interval is therefore the closest conceptual partner to the fourth. Comparing the P4 with the four-semitone major third also helps prevent errors when building chords by ear.
Frequently Asked Questions
How many semitones are in a perfect fourth?
A perfect fourth contains five semitones, or five half steps. C to F, D to G, and E to A are all examples.
What is a perfect fourth above C, D, E, and F?
A perfect fourth above C is F, above D is G, above E is A, and above F is B♭. The B♭ is necessary because F to B natural contains six semitones.
What is the difference between a perfect fourth and a perfect fifth?
A perfect fourth spans four letter names and five semitones, while a perfect fifth spans five letter names and seven semitones. They are interval inversions: inverting a perfect fourth produces a perfect fifth.
Is a perfect fourth always consonant?
No. A perfect fourth often sounds consonant melodically or between upper parts, but traditional counterpoint can treat a fourth above the bass as a dissonance requiring resolution.
What song begins with a perfect fourth?
“Amazing Grace” begins with an ascending perfect fourth. It is a common ear-training reference, although practicing from many starting notes is more reliable than memorizing a single melody.
What is the frequency ratio of a perfect fourth?
A pure or just perfect fourth has a frequency ratio of 4:3. In 12-tone equal temperament, the interval is 500 cents rather than the approximately 498 cents produced by the exact 4:3 ratio.
Vincent is a pitch detection and vocal analysis writer at OnlinePitchDetector. He focuses on pitch recognition, vocal frequency analysis, singing tools, and real-time audio testing for singers, musicians, producers, and beginners.