Number reference
255 explained.
255: two hundred fifty-five, composite; factors, prime factorization, roots, binary, hexadecimal, and digit properties.
Identity and representations
- Written form
- two hundred fifty-five
- Classification
- composite
- Factors
- 1, 3, 5, 15, 17, 51, 85, 255
- Prime factorization
- 3 × 5 × 17
- Square root
- 15.968719
- Cube root
- 6.341326
- Binary
- 11111111
- Octal
- 377
- Hexadecimal
- FF
- Roman numeral
- CCLV
- Digit sum
- 12
- Digital root
- 3
What makes 255 notable
- Factor structure. 255 breaks down into 3 distinct primes (3, 5, 17) and has 8 divisors in total, so it can be split into equal whole-number groups 6 ways beyond 1 and itself.
255 in everyday use
Two hundred fifty-five is the largest value a single byte can hold, so it is the ceiling everywhere in computing. Each red, green, and blue channel of a screen colour runs from 0 to 255, so pure white is 255, 255, 255. The subnet mask 255.255.255.0 marks which part of an IP address names the network. Older games often capped scores, lives, or levels at 255 because the counter could go no higher, and 255 is FF in hexadecimal, which is why the brightest colour code reads ffffff.
The number is 2⁸ − 1, eight binary ones in a row, which is why it is the maximum of eight bits. It factors as 3 × 5 × 17, the product of the first three Fermat primes, and consequently a regular 255-sided polygon can be constructed with compass and straightedge. Its divisors are 1, 3, 5, 15, 17, 51, 85, and 255. Its digit sum is 12, and it is a repdigit in base two and base sixteen.
Nearby numbers
How to read this page
The factor list shows every way 255 splits into equal whole-number groups — 8 divisors in total. The prime factorisation is the compact form of that same information, and the base conversions restate 255 for contexts that do not use decimal.
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