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.
Same number, different meanings
How 440 is understood across different contexts — never implying one meaning because of another.
- Mathematics
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.
- History
Concert A drifted upward through the eighteenth and nineteenth centuries as orchestras sought a brighter sound, from around 415 Hz in Baroque practice to 450 Hz and above in some halls. The rise was contested: Verdi supported an Italian government decree of 1884 setting A at 432 Hz, and France legislated a diapason normal of 435 Hz in 1859. The 1955 ISO settlement on 440 Hz ended a coordination problem that had lasted roughly two hundred years, and period-instrument ensembles still deliberately tune to the older pitches.
- Science
440 Hz means 440 vibration cycles per second. Because an octave is a 2:1 frequency ratio, the A one octave below A440 sounds at 220 Hz and the A one octave above at 880 Hz — the doubling is exact, not approximate.
- Technology & computing
440C is a high-carbon martensitic stainless steel hardenable to around 58 HRC, used for knife blades and bearings where corrosion resistance and hardness are both required.
- Sport
440 yards is a quarter of a mile and was the standard one-lap race in imperial athletics, on tracks built to that length. Metrication replaced it with 400 metres, about 2.3 metres shorter, and replaced the 440-yard track with the 400-metre one — which is why a stadium built before the change has a subtly different geometry and why records from either side of it are listed separately.
- Media & popular culture
The pitch of A above middle C under the most common tuning standard is 440 hertz (worldwide, ISO 16).
- Symbolic meaning
A widely circulated modern claim holds that tuning to 432 Hz rather than 440 Hz is more natural, healthier or better aligned with the universe, sometimes accompanied by an assertion that 440 Hz was imposed for propaganda purposes in the 1930s. There is no evidence for the physiological claims, and the historical one misstates a standardisation process that ran for a century across several countries. The belief is recorded here because a reader is likely to encounter it, not because it is supported.
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.
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
- Scientific notation
- 4.400 × 10^2
Roman numerals
C D X L
CDXL uses the subtractive pair XL: ten before fifty — fifty minus ten.
Binary
1 1 0 1 1 1 0 0 0
1 × 256 + 1 × 128 + 0 × 64 + 1 × 32 + 1 × 16 + 1 × 8 + 0 × 4 + 0 × 2 + 0 × 1 = 440
Octal
6 7 0
6 × 64 + 7 × 8 + 0 × 1 = 440
Hexadecimal
1 b 8
1 × 256 + b × 16 + 8 × 1 = 440
Read as powers of two: 256 + 128 + 32 + 16 + 8 = 440.
In historical numeral systems
Egyptian
4 coils of rope, 4 hobbles
4 × 100 + 4 × 10 = 440. The signs are simply repeated and added; where they sit on the line is a matter of layout, not value.
Babylonian
7 vertical wedges (sixties place), 2 corner wedges (units place)
7 × 60 + 20 = 440. Places are separated by a space on the tablet, with the higher place written first.
Greek (Ionic)
upsilon, then mu, marked as a numeral
upsilon-mu + keraia
upsilon + mu written in descending order and added — the letters carry their values wherever they stand, so this is addition, not place value.
Hebrew numerals
tav, then mem
tav-mem
tav (400) + mem (40) = 440, written in descending order.
Systems that simply cannot reach this value are left out. Where a script needs a font most readers do not have, the reading is given instead of the glyphs — see number systems for each system in full.
Other mathematical patterns
- Abundant number
- Happy number
- Harshad (Niven) number
Related numbers & connections
A440 sits in the octave series defined by the 2:1 frequency ratio — 220 Hz an octave below, 880 Hz an octave above.
432 Hz is promoted in some circles as a superior tuning reference; the claim has no acoustic basis and 440 remains the standard.
View 432 →Numbers Around Us
- appears inOctave frequency ratio
why?
Strength 0.50, confidence "high".
- appears inStandard athletics track lap distance
why?
Strength 0.50, confidence "high".
- appears inStandard concert pitch (A = 440 Hz)
why?
Strength 0.50, confidence "high".
History
Concert A drifted upward through the eighteenth and nineteenth centuries as orchestras sought a brighter sound, from around 415 Hz in Baroque practice to 450 Hz and above in some halls. The rise was contested: Verdi supported an Italian government decree of 1884 setting A at 432 Hz, and France legislated a diapason normal of 435 Hz in 1859. The 1955 ISO settlement on 440 Hz ended a coordination problem that had lasted roughly two hundred years, and period-instrument ensembles still deliberately tune to the older pitches.
DocumentedHistoryPeriod: 18th century to 1955
Science
440 Hz means 440 vibration cycles per second. Because an octave is a 2:1 frequency ratio, the A one octave below A440 sounds at 220 Hz and the A one octave above at 880 Hz — the doubling is exact, not approximate.
DocumentedScience
Technology & computing
440C is a high-carbon martensitic stainless steel hardenable to around 58 HRC, used for knife blades and bearings where corrosion resistance and hardness are both required.
DocumentedTechnology & computingGeography: International — AISI designations
Sport
440 yards is a quarter of a mile and was the standard one-lap race in imperial athletics, on tracks built to that length. Metrication replaced it with 400 metres, about 2.3 metres shorter, and replaced the 440-yard track with the 400-metre one — which is why a stadium built before the change has a subtly different geometry and why records from either side of it are listed separately.
DocumentedSport
Media & popular culture
The pitch of A above middle C under the most common tuning standard is 440 hertz (worldwide, ISO 16).
DocumentedMedia & popular cultureGeography: worldwide, ISO 16440 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
Symbolic meaning
A widely circulated modern claim holds that tuning to 432 Hz rather than 440 Hz is more natural, healthier or better aligned with the universe, sometimes accompanied by an assertion that 440 Hz was imposed for propaganda purposes in the 1930s. There is no evidence for the physiological claims, and the historical one misstates a standardisation process that ran for a century across several countries. The belief is recorded here because a reader is likely to encounter it, not because it is supported.
Belief / interpretationSymbolic meaningCulture: modern alternative-tuning advocacyPresented as belief or tradition, not as an established fact.
Common questions
Why is A tuned to 440 Hz?
By agreement, not by physics. Concert pitch drifted upward for two centuries — roughly 415 Hz in Baroque practice, over 450 Hz in some nineteenth-century halls — and several countries legislated their own standards along the way, France at 435 Hz in 1859 and Italy at 432 Hz in 1884. ISO 16 settled on 440 Hz in 1955. Nothing makes 440 correct; it ends a coordination problem, like agreeing which side of the road to drive on.
Is 432 Hz better than 440 Hz?
There is no evidence for it. The claim that 432 Hz is more natural or healthier, and that 440 Hz was imposed as 1930s propaganda, circulates widely and misstates a standardisation process that ran across a century and several countries. Verdi did support 432 Hz, for reasons about singers' voices rather than about the universe. Period ensembles genuinely do tune lower, and some modern orchestras tune to 442 or 444 for a brighter sound — none of which is a health claim.
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. XL is subtractive: ten before fifty — fifty minus ten. Written additively it would be CCCCXXXX, which Roman inscriptions used freely — the strict subtractive form is a later convention.
About this page's data
Mathematical facts:computed directly from the number's value — nothing to source or verify externally.
Contextual records: 7 reviewer-confirmed records, sourced and reviewed before publication.
Last reviewed: 15 July 2026