231
231 cubic inches is the volume of a US liquid gallon.
- Odd
- Composite
Where 231 fits
Why 231 is special
The figure is inherited rather than designed: the US gallon is the old English wine gallon, defined as a cylinder seven inches across and six inches deep, which works out at about 231 cubic inches. The UK redefined its gallon in 1824 and the US did not, which is why the two differ by about a fifth.
231 is part of
Factors & digit properties
- Divisors (8)
- 1, 3, 7, 11, 21, 33, 77, 231
- Prime factorisation
- 3 × 7 × 11
- Digit sum
- 6
- Digital root
- 6
Representations
- Decimal
- 231
- Scientific notation
- 2.310 × 10^2
Roman numerals
C C X X X I
Binary
1 1 1 0 0 1 1 1
1 × 128 + 1 × 64 + 1 × 32 + 0 × 16 + 0 × 8 + 1 × 4 + 1 × 2 + 1 × 1 = 231
Octal
3 4 7
3 × 64 + 4 × 8 + 7 × 1 = 231
Hexadecimal
e 7
e × 16 + 7 × 1 = 231
Read as powers of two: 128 + 64 + 32 + 4 + 2 + 1 = 231.
In historical numeral systems
Egyptian
2 coils of rope, 3 hobbles, 1 stroke
2 × 100 + 3 × 10 + 1 × 1 = 231. The signs are simply repeated and added; where they sit on the line is a matter of layout, not value.
Babylonian
3 vertical wedges (sixties place), 5 corner wedges + 1 vertical wedge (units place)
3 × 60 + 51 = 231. Places are separated by a space on the tablet, with the higher place written first.
Greek (Ionic)
sigma, then lambda, then alpha, marked as a numeral
sigma-lambda-alpha + keraia
sigma + lambda + alpha written in descending order and added — the letters carry their values wherever they stand, so this is addition, not place value.
Hebrew numerals
resh, then lamed, then alef
resh-lamed-alef
resh (200) + lamed (30) + alef (1) = 231, written in descending order.
Maya
2 bars + 1 dot (upper, twenties place) over 2 bars + 1 dot (lower, units place)
11 × 20 + 11 = 231. Places stack vertically with the smallest at the bottom, so the upper group is worth twenty times the lower.
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
- Triangular number
- Deficient number
- Hexagonal number
- Lucky number (mathematical sieve)
Related numbers & connections
Sierra Leone and Liberia were both founded as settlements for freed and formerly enslaved people, by Britain and the United States respectively.
View 232 →231 cubic inches to a US gallon and 1,728 to a cubic foot. Both are inherited definitions rather than designed ones, which is why neither is a round number.
View 1728 →Everyday life
The US liquid gallon is 231 cubic inches because it preserves the old English wine gallon — nominally a cylinder seven inches across and six deep. Britain redefined its gallon in 1824 and the United States did not, which is why the imperial gallon is about a fifth larger than the American one.
DocumentedEveryday lifeGeography: United States
Common questions
Is 231 a prime number?
No, 231 is not prime.
What are the factors of 231?
The factors of 231 are 1, 3, 7, 11, 21, 33, 77, 231.
What is 231 in Roman numerals?
231 in Roman numerals is CCXXXI.
About this page's data
Mathematical facts:computed directly from the number's value — nothing to source or verify externally.
Contextual records: 1 reviewer-confirmed record, sourced and reviewed before publication.
Last reviewed: 15 July 2026