420
A3 paper is 420 mm tall, and 420 is a cannabis reference.
- Even
- Composite
Where 420 fits
Why 420 is special
The two are unrelated. A3 is 297 by 420 mm, twice A4. The cannabis meaning traces to a group of Californian students who met at 4:20 pm in 1971, an origin their own accounts document and which displaced several invented explanations.
Same number, different meanings
How 420 is understood across different contexts — never implying one meaning because of another.
- Mathematics
The two are unrelated. A3 is 297 by 420 mm, twice A4. The cannabis meaning traces to a group of Californian students who met at 4:20 pm in 1971, an origin their own accounts document and which displaced several invented explanations.
- Everyday life
A3 is 297 by 420 mm — an A4 sheet doubled along its short side. Every step up the series doubles the area while keeping the shape, which is why enlarging A4 artwork to A3 needs no cropping or rescaling.
- History
The term is generally traced to a group of students at San Rafael High School in California around 1971, who used 4:20 as the time to meet. The competing explanation that it is a police radio code has been repeatedly checked and found to be unsupported.
- Culture
The twentieth of April is observed as an annual gathering in several countries, and legislatures have on occasion scheduled cannabis-related votes on or near it. The observance grew from the slang rather than the other way round.
Factors & digit properties
- Divisors (24)
- 1, 2, 3, 4, 5, 6, 7, 10, 12, 14, 15, 20, 21, 28, 30, 35, 42, 60, 70, 84, 105, 140, 210, 420
- Prime factorisation
- 2^2 × 3 × 5 × 7
- Digit sum
- 6
- Digital root
- 6
Representations
- Decimal
- 420
- Scientific notation
- 4.200 × 10^2
Roman numerals
C D X X
CDXX uses the subtractive pair CD: a hundred before five hundred — five hundred minus a hundred.
Binary
1 1 0 1 0 0 1 0 0
1 × 256 + 1 × 128 + 0 × 64 + 1 × 32 + 0 × 16 + 0 × 8 + 1 × 4 + 0 × 2 + 0 × 1 = 420
Octal
6 4 4
6 × 64 + 4 × 8 + 4 × 1 = 420
Hexadecimal
1 a 4
1 × 256 + a × 16 + 4 × 1 = 420
Read as powers of two: 256 + 128 + 32 + 4 = 420.
In historical numeral systems
Egyptian
4 coils of rope, 2 hobbles
4 × 100 + 2 × 10 = 420. 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), empty units place
7 × 60 + 0 = 420. Places are separated by a space on the tablet, with the higher place written first. The second place is empty, and this is precisely the case the early system could not write unambiguously — the same wedges alone would also read as 1.
Greek (Ionic)
upsilon, then kappa, marked as a numeral
upsilon-kappa + keraia
upsilon + kappa 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 kaf
tav-kaf
tav (400) + kaf (20) = 420, 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
- Harshad (Niven) number
Related numbers & connections
A3 is 297 by 420 mm, an A4 sheet doubled along its short side. Each step up the series doubles the area and preserves the shape.
View 297 →Both are numbers whose meaning online is social rather than numerical, and both are used deliberately in pricing and version numbers.
View 69 →The term is traced to a group of California students meeting at 4:20 in about 1971.
View 1971 →Everyday life
A3 is 297 by 420 mm — an A4 sheet doubled along its short side. Every step up the series doubles the area while keeping the shape, which is why enlarging A4 artwork to A3 needs no cropping or rescaling.
DocumentedEveryday lifeGeography: International outside North America
History
The term is generally traced to a group of students at San Rafael High School in California around 1971, who used 4:20 as the time to meet. The competing explanation that it is a police radio code has been repeatedly checked and found to be unsupported.
DocumentedHistoryGeography: United States, then internationalPeriod: 1971–
Culture
The twentieth of April is observed as an annual gathering in several countries, and legislatures have on occasion scheduled cannabis-related votes on or near it. The observance grew from the slang rather than the other way round.
DocumentedCultureGeography: United States, Canada and elsewherePeriod: 1990s–
Common questions
Is 420 a prime number?
No, 420 is not prime.
What are the factors of 420?
The factors of 420 are 1, 2, 3, 4, 5, 6, 7, 10, 12, 14, 15, 20, 21, 28, 30, 35, 42, 60, 70, 84, 105, 140, 210, 420.
What is 420 in Roman numerals?
420 in Roman numerals is CDXX. CD is subtractive: a hundred before five hundred — five hundred minus a hundred. Written additively it would be CCCCXX, 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: 3 reviewer-confirmed records, sourced and reviewed before publication.
Last reviewed: 15 July 2026