A bit is the smallest unit of data in computing — a single binary digit, either 0 or 1. A byte is a group of 8 bits and can represent 256 distinct values (0 through 255). Every file, image, and message on your computer is measured in bytes or multiples of bytes.
How Bits Become Bytes
Eight bits wired together form one byte. That grouping was not arbitrary: an 8-bit byte can represent all 128 ASCII characters and leave room for an extended set of 128 more. The choice became the global standard in the 1960s and has not changed.
A single byte can hold:
- One ASCII character (the letter A, a digit, a space)
- A color intensity value from 0 to 255 (used in RGB images)
- A raw audio sample in low-quality audio formats
With 8 bits and two possible states per bit, the number of unique patterns a byte can hold is 2⁸ = 256. That arithmetic — 2 raised to the number of bits — applies to every unit in the table below.
Storage Units
| Unit | Abbreviation | Size | Approximate size |
|---|---|---|---|
| Bit | b | 1 binary digit | One switch |
| Nibble | — | 4 bits | One hex digit |
| Byte | B | 8 bits | One character |
| Kilobyte | KB | 1,000 bytes (SI) / 1,024 bytes (binary) | A short email |
| Megabyte | MB | ~1 million bytes | A JPEG photo |
| Gigabyte | GB | ~1 billion bytes | A movie file |
| Terabyte | TB | ~1 trillion bytes | A hard drive |
| Petabyte | PB | ~1 quadrillion bytes | Large data center |
The SI (metric) system defines kilo as exactly 1,000, while the binary tradition uses 1,024 (2¹⁰). Both conventions appear in the wild. The IEC introduced the terms kibibyte (KiB), mebibyte (MiB), and gibibyte (GiB) for the strict powers-of-2 versions, but consumer software and hardware still uses KB, MB, and GB for both.
Bits vs. Bytes in Everyday Contexts
Internet speed is measured in megabits per second (Mbps) or gigabits per second (Gbps). File size is measured in megabytes (MB) or gigabytes (GB). Because there are 8 bits per byte, you can convert between them:
Download time (seconds) = File size in megabytes × 8 ÷ Speed in megabits per second
Example: A 500 MB file on a 100 Mbps connection takes 500 × 8 ÷ 100 = 40 seconds to download.
What a Byte Looks Like in Binary
The byte value 65, which represents the capital letter A in ASCII, looks like this in binary:
| Bit 7 | Bit 6 | Bit 5 | Bit 4 | Bit 3 | Bit 2 | Bit 1 | Bit 0 |
|---|---|---|---|---|---|---|---|
| 0 | 1 | 0 | 0 | 0 | 0 | 0 | 1 |
| 128 | 64 | 32 | 16 | 8 | 4 | 2 | 1 |
Active bits: 64 + 1 = 65. See How to Read Binary for the full walkthrough of positional values.
Word, Double Word, and Larger Units
Beyond bytes, CPUs group bytes into larger chunks:
- Word: typically 2 bytes (16 bits) on older architectures
- Double word (DWORD): 4 bytes (32 bits)
- Quad word (QWORD): 8 bytes (64 bits)
A 64-bit processor moves 8 bytes of data per clock cycle. That wider data path is why 64-bit operating systems handle large files and memory much faster than the 32-bit systems they replaced.
Use the binary translator to convert any decimal number to its binary byte representation, or read Binary vs. Hexadecimal to see how bytes are often written more compactly as two-digit hex values.