255 (number)

← 254 255 256 →
← 250 251 252 253 254 255 256 257 258 259 → List of numbers Integers ← 0 100 200 300 400 500 600 700 800 900 →
Cardinal	Two hundred [and] fifty-five
Ordinal	th
Factorization	$255=3\cdot 5\cdot 17$
Greek numeral	ΣΝΕ´
Roman numeral	CCLV
Binary	111111112
Ternary	1001103
Senary	11036
Octal	3778
Duodecimal	19312
Hexadecimal	FF16

255 (two hundred [and] fifty-five, CCLV) is the natural number following 254 and preceding 256.

In mathematics

Its factorization makes it a sphenic number. Since 255 = 2⁸ - 1, it is a Mersenne number, and the fourth such number not to be a prime number. It is a perfect totient number, the smallest such number to be neither a power of three nor thrice a prime.

In base 10, it is a self number.

255 is a repdigit in base 2 (11111111) in base 4 (3333), and in base 16 (FF).

In Astronomy

255 is the number of days in a lunar year. Given that there are 12 months in a lunar year and that each month starts and ends on each full moon, the total number of days would equal 255.

In computing

255 is a special number in some tasks having to do with computing. This is the maximum value representable by an eight-digit binary number, and therefore the maximum representable by an unsigned 8-bit byte (the most common size of byte, also called octet), the smallest common variable size used in high level programming languages (bit being smaller, but rarely used for value storage). The range is 0 to 255, which is 256 total values.

$255=2^{8}-1={\mbox{FF}}_{16}=11111111_{2}.$

For example, 255 is the maximum value

• that can be assigned to elements in the 24-bit RGB color model, since each color channel is allotted eight bits.
• of any dotted quad in an IP address.
• of the Alpha blending scale in Delphi (255 being 100% visible and 0 being fully transparent)

This number occurs especially frequently in video games when a small number is needed, as in the following examples:

• In The Legend of Zelda for the Nintendo Entertainment System, the maximum number of Rupees (the currency of the game) is 255.
• In Metroid, 255 is the maximum number of missiles Samus Aran can hold.
• 255 was also the number of missiles in Metroid Prime 2: Echoes for the Nintendo Gamecube and Metroid Prime 3: Corruption for Wii.
• In the Madden NFL series, the maximum points you can score is 255. If more points are scored, the game score remains at 255 regardless.
• In Starcraft, the maximum number of kills shown for a unit, and the maximum number of armor and attack upgrades, are both 255. In the case of the Zerg Ultralisk with the Brood War enhanced armor upgrade, having 257 armor restarts the armor to 0.
• In Square Enix's Final Fantasy series, it is often the maximum value for any given stat.
• In Final Fantasy 8, it is the maximum number to which you can boost your Guardian Forces during the attack video cut scenes.
• In Pac-Man, all levels past #255 are glitched.
• In World of Warcraft although the game level cap is 80, the engine supports up to 255.
• In the Pokémon video games for the Nintendo DS and Game Boy, 255 is the maximum number of Effort Values a Pokemon can have in a certain stat. Through the use of glitches, a Pokemon can also be raised up to level 255, after which it reverts to level 0.
• In Harvest Moon, the maximum amount of friend points in a villager is 255.
• In Star Ocean The Second Story, it is the maximum level all characters can reach.
• In Telefang, the theoretical highest value of any stat that a Denjuu can have is 255 (though this never gets this high in practice, but can be seen by hacking). Also, the most amount of damage that can be dealt is 255, which happens inevitably in a boss battle late in the game. These limits are also in Telefang 2 as well.

The usage of 8 bits for storage in older videogames has had the consequence of it appearing as a hard limit in many videogames. It was often used for numbers where casual gameplay would not cause anyone to exceed the number. However in most situations it is reachable given enough time. This can cause many other peculiarities similar to the above listed to appear when the number wraps back to 0.

This number could be interpreted by a computer as -1 if a programmer is not careful about which 8-bit values are signed and unsigned, and the two's complement representation of -1 in a signed byte is equal to that of 255 in an unsigned byte.