Number reference
128 explained.
128: one hundred twenty-eight, composite, power of two; factors, prime factorization, roots, binary, hexadecimal, and digit properties.
Identity and representations
- Written form
- one hundred twenty-eight
- Classification
- composite
- Factors
- 1, 2, 4, 8, 16, 32, 64, 128
- Prime factorization
- 2 × 2 × 2 × 2 × 2 × 2 × 2
- Square root
- 11.313708
- Cube root
- 5.039684
- Binary
- 10000000
- Octal
- 200
- Hexadecimal
- 80
- Roman numeral
- CXXVIII
- Digit sum
- 11
- Digital root
- 2
What makes 128 notable
- Power of two. 128 = 2^7, which is why it shows up in memory sizes, image dimensions, and anything that repeatedly halves or doubles.
128 in everyday use
One hundred twenty-eight is two to the seventh power and the size of the original ASCII character set, which assigned codes 0 through 127. Signed bytes run from −128 to 127, so 128 is the first value that will not fit. The number labels 128-bit encryption keys, 128 kbps audio streams, and 128 GB storage tiers, all because computer sizes double. There are also 128 fluid ounces in a US gallon, a fact that makes American liquid measures halve neatly all the way down to the ounce.
As a power of two it has exactly eight divisors, 1, 2, 4, 8, 16, 32, 64, and 128, and it is written 10000000 in binary, a one followed by seven zeros. It is the largest number that cannot be written as a sum of distinct squares — every number above 128 can be. Its digit sum is 11, and it is the seventh term of the sequence 2, 4, 8, 16, 32, 64, 128 that appears whenever anything doubles seven times.
Nearby numbers
How to read this page
The factor list shows every way 128 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 128 for contexts that do not use decimal.
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