440
440 Hz ("A440") is the standard reference pitch most orchestras and instrument makers tune the note A above middle C to.
- Even
- Composite
Where 440 fits
Why 440 is special
440's significance is entirely conventional, not physical or mathematical: the ISO 16 standard formalised 440 Hz as concert pitch in 1955, but this was itself a compromise among earlier tuning standards that ranged roughly 415-450 Hz across different orchestras, eras, and countries — some ensembles today still deliberately tune slightly higher (e.g. 442-444 Hz) for a brighter sound. There is no physical or mathematical reason A must be exactly 440 Hz; it is a coordination standard, the musical equivalent of countries agreeing to drive on a particular side of the road.
Not just a mathematical number
440is also used in ways where ordinary arithmetic doesn't apply — each listed below with what genuinely does and doesn't follow from it.
- Mathematical number
A genuine quantity — its mathematical properties (prime, square, factors, and so on) are real facts about it.
A genuine quantity that ordinary arithmetic applies to — it can be prime, even, a perfect square, added to another number meaningfully, and so on.
- Measurement
Also used as a measurement — Standard concert pitch (A = 440 Hz).
A quantity expressed against a defined unit or standard (24 hours in a day, 60 seconds in a minute) — arithmetic is meaningful, but the specific value is a fixed convention of the measuring system, not a discovered mathematical property.
440 is part of
Factors & digit properties
- Divisors (16)
- 1, 2, 4, 5, 8, 10, 11, 20, 22, 40, 44, 55, 88, 110, 220, 440
- Prime factorisation
- 2^3 × 5 × 11
- Digit sum
- 8
- Digital root
- 8
Representations
- Decimal
- 440
- Binary
- 110111000
- Octal
- 670
- Hexadecimal
- 1b8
- Roman numeral
- CDXL
- Scientific notation
- 4.400 × 10^2
Other mathematical patterns
- Abundant number
- Happy number
- Harshad (Niven) number
Related numbers & connections
440 Hz is the ISO 16 standard reference frequency for concert pitch A.
Numbers Around Us
- appears inStandard concert pitch (A = 440 Hz)
why?
Strength 0.50, confidence "high".
Media & popular culture
440 Hz ("A440") was formalised as standard international concert pitch by ISO 16 in 1955 — the frequency most orchestras and instrument makers tune the note A above middle C to, though real historical and regional variation exists.
DocumentedMedia & popular culture440 Hz ("A440") was formalised as standard international concert pitch by ISO 16 in 1955 — the frequency most orchestras and instrument makers tune the note A above middle C to, though real historical and regional variation exists.
DocumentedMedia & popular culture
Common questions
Is 440 a prime number?
No, 440 is not prime.
What are the factors of 440?
The factors of 440 are 1, 2, 4, 5, 8, 10, 11, 20, 22, 40, 44, 55, 88, 110, 220, 440.
What is 440 in Roman numerals?
440 in Roman numerals is CDXL.
About this page's data
Mathematical facts:computed directly from the number's value — nothing to source or verify externally.
Contextual records: 2 reviewer-confirmed records, sourced and reviewed before publication.
Last reviewed: 15 July 2026