From phone storage to internet speeds to cloud backup — data storage units appear everywhere in modern life. Here is a clear explanation of each unit and how they relate to each other.
The Hierarchy of Data Units
| Unit | Symbol | Decimal (SI) | Common Use |
|---|---|---|---|
| Bit | bit | 1 bit | Network speeds |
| Byte | B | 8 bits | Base unit for storage |
| Kilobyte | KB | 1,000 bytes | Text files, small images |
| Megabyte | MB | 1,000,000 bytes | Photos, songs |
| Gigabyte | GB | 1,000,000,000 bytes | Apps, videos, phone storage |
| Terabyte | TB | 1,000,000,000,000 bytes | Hard drives, cloud storage |
| Petabyte | PB | 1,000 TB | Data centres |
Decimal vs Binary
There is an important distinction in storage measurement. Hard drive manufacturers use the decimal (SI) system where 1 KB = 1,000 bytes. Operating systems like Windows and older macOS use the binary system where 1 KiB (kibibyte) = 1,024 bytes.
This is why a "1 TB" hard drive shows as ~931 GB when connected to Windows — the OS reports in binary (GiB) but the drive is labelled in decimal (GB).
Bits vs Bytes — Internet Speeds
Internet speeds are measured in bits per second (bps), while file sizes use bytes. There are 8 bits in 1 byte.
- 100 Mbps internet → downloads at ~12.5 MB/s (megabytes per second)
- 1 Gbps internet → downloads at ~125 MB/s
Real-World File Sizes
| Item | Typical Size |
|---|---|
| Text document (1 page) | ~30 KB |
| Smartphone photo (JPEG) | 3–8 MB |
| MP3 song (3 min) | 3–8 MB |
| HD movie (2 hr) | 4–8 GB |
| 4K movie (2 hr) | 50–100 GB |
| Typical smartphone app | 50–200 MB |