The short version
A bit is a single binary digit — one 0 or one 1. A byte is a group of eight bits. That's the whole difference, but the two units are used for different jobs: bits measure speed (how fast data moves), while bytes measure size (how much data you have). Internet plans are sold in megabits per second (Mbps); files are measured in megabytes (MB). Note the capitalization convention: a lowercase b means bit (Mb), an uppercase B means byte (MB).
Why eight?
There's nothing mathematically inevitable about eight — early computers used 6-bit and even 12-bit groupings. Eight won for a practical reason: it's enough to encode a full character set. The ASCII standard needed 7 bits for 128 characters; an 8-bit byte held a character with one bit to spare (used for error checking). When IBM's System/360 mainframe standardized the 8-bit byte in the 1960s, the industry followed, and it stuck. Half a byte — four bits — is playfully called a nibble, which is exactly one hexadecimal digit.
Scaling up: KB, MB, GB…
Bytes scale with metric-style prefixes, and this is where it gets messy. There are two competing definitions:
| Unit | Decimal (SI) | Binary (traditional) |
|---|---|---|
| Kilobyte (KB) | 1,000 bytes | 1,024 bytes |
| Megabyte (MB) | 1,000,000 bytes | 1,048,576 bytes |
| Gigabyte (GB) | 1,000,000,000 bytes | 1,073,741,824 bytes |
| Terabyte (TB) | 10¹² bytes | 2⁴⁰ bytes |
Hard-drive manufacturers use the decimal definition (1,000), while operating systems traditionally used the binary one (1,024) — which is why a "1 TB" drive shows up as only ~931 GB in Windows. The gap grows with size: at the terabyte level it's about 10%. To end the confusion, official binary names exist — kibibyte (KiB), mebibyte (MiB), gibibyte (GiB) — meaning exactly 1024-based units. You'll see them in Linux tools and technical documentation.
Bits for speed, bytes for size
The practical rule: network speeds are in bits, file sizes are in bytes. A "100 Mbps" connection moves 100 million bits per second — divide by 8 to get roughly 12.5 megabytes per second of actual downloads. (Real throughput is a bit lower still, because protocols add their own overhead.) So when your 800 MB game downloads at "100 megabits", expect about a minute, not eight seconds. The industry isn't trying to confuse you — engineers genuinely think of a network as a pipe carrying a stream of bits — but now you know how to translate.
How much is a byte, really?
One byte holds values from 0 to 255 — enough for one text character, one pixel's red/green/blue channel, or a tiny number. Scale that up and the numbers get relatable fast:
| Amount | Roughly equals |
|---|---|
| 1 byte | one character (e.g. "A") |
| 1 KB | a short paragraph of text |
| 1 MB | a small photo, or a 500-page plain-text book |
| 1 GB | ~15 minutes of HD video |
| 1 TB | ~250,000 photos or 500 hours of video |
Try it yourself
See bytes in action: convert text to binary and count the bits — every character becomes exactly 8 of them.
Key takeaways
- A bit is one binary digit; a byte is eight bits.
- Lowercase "b" = bit (Mb), uppercase "B" = byte (MB) — the case matters.
- Bits measure speed (Mbps), bytes measure size (MB).
- A kilobyte is 1,000 bytes to drive makers but 1,024 to old-school software — the source of "missing" disk space.
- Divide bits by 8 to estimate bytes: 100 Mbps ≈ 12.5 MB/s downloads.
Frequently asked questions
Why is a byte 8 bits?
Mostly historical convention. Eight bits was enough to encode a text character plus a little room to spare, and IBM's System/360 mainframe made the 8-bit byte an industry standard in the 1960s.
Is a kilobyte 1000 or 1024 bytes?
Both, depending on context. Storage makers use 1000 (decimal kilo); operating systems traditionally use 1024 (binary). The unambiguous names are kilobyte (1000) and kibibyte (1024).
Why is internet speed measured in bits, not bytes?
Because networks move individual bits along a wire, so bits per second describes the raw transmission rate. Divide by 8 to estimate bytes per second — a 100 Mbps line moves roughly 12.5 megabytes per second.
How many bytes are in a gigabyte?
One billion bytes (1,000,000,000) by the decimal definition used by drive manufacturers, or 1,073,741,824 bytes (1024³) by the binary definition — a 7% difference that explains shrinking hard drives.