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Data Size Units Explained: KB, MB, GB, TB and Beyond
3 min read · Last updated: 2026-05-08
The byte is the base unit
1 byte (B) = 8 bits. It is the fundamental unit for measuring all digital data sizes.
SI units (base-1000) vs binary units (base-1024)
The core source of confusion is whether 1 KB means 1,000 B or 1,024 B. The official standards are:
| Unit | Symbol | Exact value | Typical use |
|---|---|---|---|
| Kilobyte | KB (SI) | 1,000 B | Storage manufacturers, network speeds |
| Kibibyte | KiB (IEC) | 1,024 B | OS internals, file systems |
| Megabyte | MB (SI) | 1,000,000 B | Storage specs |
| Mebibyte | MiB (IEC) | 1,048,576 B | OS display |
| Gigabyte | GB (SI) | 1,000,000,000 B | Drive capacity labels |
| Gibibyte | GiB (IEC) | 1,073,741,824 B | OS reported capacity |
| Terabyte | TB (SI) | 10¹² B | Large storage |
| Tebibyte | TiB (IEC) | 2⁴⁰ B | Servers / data centers |
Why does a drive appear smaller in the OS?
Manufacturers label drives using SI (1 GB = 1,000,000,000 B), but operating systems (Windows) report capacity in GiB (1,073,741,824 B). A 1 TB drive shows as roughly 931 GiB in the OS.
Calculation: 1,000,000,000,000 ÷ 1,073,741,824 ≈ 931
Beware of confusion with network speed units
Internet speeds are typically measured in Mbps (Megabits per second), not megabytes. 1 MB = 8 Mb. A 100 Mbps connection downloads a 1 GB file in approximately 80 seconds.
Key takeaways
- Drive manufacturers use SI (×1000); operating systems use binary (×1024).
- Precise notation: KiB, MiB, GiB (binary) vs KB, MB, GB (SI).
- Do not confuse network speed (Mbps) with file size (MB). 1 Byte = 8 bits.