256 (two hundred [and] fifty-six) is the natural number following 255 and preceding 257.

256 is a composite number, with the factorization 256 = 2⁸, which makes it a power of two.

• 256 is 4 raised to the 4th power, so in tetration notation, 256 is ²4.^[1]
  • 256 is the value of the expression ${\displaystyle n^{n}}$, where ${\displaystyle n=4}$.
• 256 is a perfect square (16²).
• 256 is the only 3-digit number that is zenzizenzizenzic. It is 2 to the 8th power or ${\displaystyle ((2^{2})^{2})^{2}}$.
• 256 is the lowest number that is a product of eight prime factors.
• 256 is the number of parts in all compositions of 7.^[2]

One octet (in most cases one byte) is equal to eight bits and has 2⁸ or 256 possible values, counting from 0 to 255. The number 256 often appears in computer applications (especially on 8-bit systems) such as:

• The typical number of different values in each color channel of a digital color image (256 values for red, 256 values for green, and 256 values for blue used for 24-bit color) (see color space or Web colors).
• The number of colors available in a GIF or a 256-color (8-bit) bitmap.
• The number of characters in extended ASCII^[3] and Latin-1.^[4]
• The number of columns available in a Microsoft Excel worksheet until Excel 2007.^[5]
• The split-screen level in Pac-Man, which results from the use of a single byte to store the internal level counter.
• A 256-bit unsigned integer can represent up to 115,792,089,237,316,195,423,570,985,008,687,907,853,269,984,665,640,564,039,457,584,007,913,129,639,936 values.^[6]
• The number of bits in the SHA-256 cryptographic hash.
• The branding number of Nvidia's GeForce 256.