Standard A440 quick reference
- A4 reference
- 440 Hz
- Relative to A440
- 0.0 cents
- Meter range
- A0–C8
What this reference means
The ISO standard tuning frequency and the usual reference for modern pianos.
Use A440 unless an ensemble, recording, or technician specifies another reference.
Sample calculated key targets
The meter applies the same formula to all 88 keys. These sample values make the selected reference visible before microphone use.
| Piano key | Note | MIDI | Frequency |
|---|---|---|---|
| 1 | A0 | 21 | 27.50 Hz |
| 40 | C4 | 60 | 261.63 Hz |
| 49 | A4 | 69 | 440.00 Hz |
| 52 | C5 | 72 | 523.25 Hz |
| 88 | C8 | 108 | 4186.01 Hz |
Need every key? Open the interactive 88-key frequency chart.
Instrument safety and scope
A browser meter can check pitch, but it cannot set unisons, stretch, or tuning stability.
Method and sources
Each displayed target uses frequency = 440 × 2((MIDI − 69) / 12). This is a transparent equal-temperament calculation. A real piano's string inharmonicity leads technicians to stretch octaves, so a browser target is not a complete tuning curve.
Standard A440 FAQ
What does Standard A440 mean?
The ISO standard tuning frequency and the usual reference for modern pianos. Use A440 unless an ensemble, recording, or technician specifies another reference.
Does this page really use A4 = 440 Hz?
Yes. Every key target is recalculated from A4 = 440 Hz using the 12-tone equal-temperament formula. The selected reference changes both automatic note matching and fixed-key targets.
Can I retune an acoustic piano to 440 Hz with this page?
This page can measure and compare pitch, but it cannot assess the instrument's structure, unisons, stretch, or stability. Ask a qualified piano technician before changing an acoustic piano's overall pitch.