Bits vs bytes
A bit is a single binary digit, a 0 or a 1; a byte is a group of 8 bits. Networks measure speed in bits (b), while files, memory and drives are sized in bytes (B), so converting between them always means multiplying or dividing by 8.
What a bit and a byte are
A bit is the smallest unit of digital information: one binary digit with two possible values. A byte is 8 bits, enough for 256 different values, because 2 × 2 × 2 × 2 × 2 × 2 × 2 × 2 = 256.
The 8-bit byte became the standard because it is a convenient size for a character of text and for addressing memory. Standards documents sometimes say "octet" to mean exactly 8 bits, because early computers used bytes of other sizes. Today a byte is 8 bits everywhere you are likely to meet one.
1 B = 8 b 1 kB = 1,000 B = 8,000 b 1 MB = 1,000,000 B = 8,000,000 b
The bytes to bits converter and the bits to bytes converter handle any value, including binary units.
Why networks count bits and storage counts bytes
A network link sends data one symbol after another down a wire, a fibre or a radio channel, so its capacity is naturally counted in bits per second. That convention runs through networking: Ethernet ports are rated at 1 Gbps or 10 Gbps, USB 2.0 at 480 Mbps, and home plans in Mbps.
Storage and memory are organised in bytes. A file is a sequence of bytes, memory addresses point to bytes, and the software that saves or copies files reports sizes and speeds in bytes: kB, MB, GB and MB/s.
Both conventions are sensible on their own. The trouble starts when you compare a plan in Mbps with a file in GB, which is why Mbps vs MB/s is one of the most common points of confusion.
Prefixes: decimal (kB, MB) and binary (KiB, MiB)
The prefixes kilo, mega, giga and tera are SI prefixes and mean powers of 1,000. Because computer memory comes in powers of 2, software long used the same names for powers of 1,024. To remove the ambiguity, the IEC defined separate binary prefixes: kibi (Ki), mebi (Mi), gibi (Gi) and tebi (Ti).
| Decimal unit | Bytes | Binary unit | Bytes | Binary is larger by |
|---|---|---|---|---|
| 1 kB | 1,000 | 1 KiB | 1,024 | 2.4% |
| 1 MB | 1,000,000 | 1 MiB | 1,048,576 | 4.9% |
| 1 GB | 1,000,000,000 | 1 GiB | 1,073,741,824 | 7.4% |
| 1 TB | 1,000,000,000,000 | 1 TiB | 1,099,511,627,776 | 10.0% |
The gap grows with each step, which is why it hardly matters for a small file and matters a lot for a large drive. Bit prefixes in networking are always decimal: 1 Mbps is exactly 1,000,000 bits per second.
Why a 1 TB drive shows about 931 GB
Drive makers use decimal units, so a 1 TB drive holds 1,000,000,000,000 bytes. Some operating systems, Windows among them, count in powers of 1,024 but still write "GB". Divide by 1,073,741,824 and you get 931.3, so the drive appears as "931 GB" although nothing is missing. A 500 GB drive shows as about 465.7 in the same way.
The same effect applies to downloads. A file that one program lists as "1 GB" may be 1 GiB, which is 1,073,741,824 bytes, or 8,589,934,592 bits. At 100 Mbps that takes about 85.9 seconds rather than the 80 seconds a decimal gigabyte takes. The calculators on this site keep the two apart: pick GB or GiB explicitly.
Writing units without ambiguity
| Symbol | Means | Note |
|---|---|---|
| b | bit | Lowercase b |
| B | byte (8 bits) | Uppercase B |
| kB | kilobyte, 1,000 bytes | Many apps write "KB", sometimes meaning 1,024 bytes |
| KiB | kibibyte, 1,024 bytes | Binary, unambiguous |
| Mb / Mbps | megabit / megabits per second | Network speeds |
| MB / MB/s | megabyte / megabytes per second | File sizes and download apps |
Two quick sanity checks cover most real cases. A value with a lowercase b is 8 times smaller than the same number with an uppercase B. And if a figure matters, such as a drive size or a transfer estimate, ask whether it is decimal or binary before comparing. The bytes per second to Mbps converter shows both families side by side.
Key takeaways
- A byte is 8 bits. Lowercase b means bit, uppercase B means byte.
- Networks count bits per second; files, memory and drives count bytes.
- kB, MB, GB are powers of 1,000; KiB, MiB, GiB are powers of 1,024. The gap is 7.4% at the gigabyte level.
- A 1 TB drive shows about 931 "GB" in software that counts in binary units, with nothing missing.
Frequently asked questions
Why is a byte 8 bits?
Eight bits give 256 possible values, enough for a character of text, and powers of two suit computer hardware. The 8-bit byte became the dominant size decades ago and is now universal.
Is a kilobyte 1,000 or 1,024 bytes?
Under SI and IEC rules, 1 kB is 1,000 bytes and 1 KiB is 1,024 bytes. Some software still uses "KB" for 1,024 bytes, so check which one a program means.