What note is that frequency?
Every octave doubles the frequency, and every semitone multiplies it by the twelfth root of two.
Almost exactly A4
440 Hz is higher than 4 of the 9 references on this page.
Reference figures are measurements and are rounded; the unit conversion behind them is exact.
| Reference | Size | Yours ÷ theirs | Note |
|---|---|---|---|
| A0 | 27.5 Hz | 16× | The lowest piano key |
| A1 | 55 Hz | 8× | |
| A2 | 110 Hz | 4× | |
| A3 | 220 Hz | 2× | |
| A4 | 440 Hz | 1× | Concert pitch |
| A5 | 880 Hz | 0.5× | |
| A6 | 1,760 Hz | 0.25× | |
| A7 | 3,520 Hz | 0.125× | |
| C8 | 4,186 Hz | 0.105× | The highest piano key |
Worth knowing
- A piano spans 27.5 Hz to 4 186 Hz — just over seven octaves, or a factor of 152 in frequency.
- A semitone is a frequency ratio of 2^(1/12), about 1.0595. Twelve of them multiply to exactly 2.
Frequently asked
How do I work out a note’s frequency?
Multiply 440 by 2^(n/12), where n is the number of semitones above A4 — negative for below. A4 + 3 semitones is 440 × 2^(3/12) = 523.25 Hz, which is C5.
What is equal temperament?
Dividing the octave into twelve equal frequency ratios, so every key sounds the same. It makes every interval except the octave slightly out of tune, which is the price of playing in all keys.