Music & Audio

Note Frequency

Calculate the exact Hz frequency of any musical note relative to A440.

Every musical note has a precise frequency in hertz. This calculator uses the equal temperament formula to find the exact pitch of any note by specifying the number of semitones above or below A4 (440 Hz), the universal tuning standard.

Enter your numbers

Semitones from A4 (±)

A4=0, A#4=1, B4=2, C5=3, C4=-9, Middle C=C4=-9

Results update as you change the inputs. Calculations run in your browser.

Frequency

440.00 Hz

note: A
wavelength: 0.780 m (in air)
midi Note: 69 MIDI

See the formula

Formula and method

f = 440 × 2^(n/12)

Equal temperament divides the octave into 12 equal semitones. Each semitone is a frequency ratio of 2^(1/12) ≈ 1.05946. Starting from A4 at 440 Hz, you can calculate any note precisely. A440 is the international standard (ISO 16).

Worked examples

Middle C (C4)

Semitones from A4 (±):: -9

Frequency: 261.63 Hz

Concert A (A4)

Semitones from A4 (±):: 0

Frequency: 440.00 Hz

Assumptions and limits

A4 = 440 Hz (ISO standard)
Equal temperament (12-TET)

This tool provides an educational estimate. Rules, rates and personal circumstances can change the answer. Review the assumptions before relying on a result. Report a correction.

Common mistakes to avoid

Confusing note number with octave number — Middle C is C4, which is -9 semitones from A4.
Using 432 Hz tuning — some prefer A432 but 440 Hz is the international standard for most professional work.
Forgetting that MIDI note 69 = A4 = 440 Hz — the reference point for MIDI synthesis.

Frequently asked questions

What is Middle C frequency?

Middle C (C4) is 261.63 Hz. It is 9 semitones below A4, so: 440 × 2^(-9/12) = 261.63 Hz.

What is the difference between 432 Hz and 440 Hz tuning?

432 Hz tuning means A4 = 432 Hz instead of 440 Hz. All notes shift down by about 31 cents. This is a preference choice with no scientific evidence of health benefits. 440 Hz is the universal broadcast and recording standard.

How many audible notes are there?

Human hearing spans roughly 20 Hz to 20,000 Hz. On a standard piano (A0 at 27.5 Hz to C8 at 4186 Hz) that is 88 notes. This calculator covers ±48 semitones (8 octaves centered on A4).