Music is built from 12 notes that repeat in every octave. Tap each key below to hear it.
Every musical note is a sound wave vibrating at a specific frequency, measured in Hertz (Hz) — cycles per second. The faster the vibration, the higher the pitch.
The international tuning standard sets A4 = 440 Hz. From this single reference pitch, all other notes are derived mathematically using 12-Tone Equal Temperament.
The Equal Temperament Formula
Each successive semitone multiplies the frequency by 2^(1/12) ≈ 1.0595
The general formula: f = 440 × 2^(n/12) where n is the number of semitones from A4.
After 12 semitones (one octave), the frequency exactly doubles: A4 (440 Hz) → A5 (880 Hz). This is why octaves sound like “the same note, higher.”
Why Octaves Sound the Same
When you double a frequency, the sound waves align perfectly — every other wave peak matches. Our ears perceive this strong harmonic relationship as the “same note,” just higher or lower. This is why the 12-note pattern repeats in every octave.
Click any row to hear the note
| Note | Frequency (Hz) |
|---|---|
| A4(reference) | 440.00 |
| A#/Bb4 | 466.16 |
| B4 | 493.88 |
| C5 | 523.25 |
| C#/Db5 | 554.37 |
| D5 | 587.33 |
| D#/Eb5 | 622.25 |
| E5 | 659.26 |
| F5 | 698.46 |
| F#/Gb5 | 739.99 |
| G5 | 783.99 |
| G#/Ab5 | 830.61 |
| A5(octave) | 880.00 |
Notes are named with a letter (A-G) plus an octave number. C4 is “Middle C” — the note at the center of a piano keyboard and the reference point for reading music.
The 12 notes are: C, C#, D, D#, E, F, F#, G, G#, A, A#, B — then the pattern repeats at the next octave. Notes with a # (sharp) or b (flat) are called accidentals and correspond to the black keys on a piano.
All 12 notes — tap to play