File Size Units Explained
Understanding KB vs KiB, MB vs MiB, and all storage measurements
Quick Summary:
There are two systems for measuring file sizes: Decimal (SI) using powers of 1000, and Binary (IEC) using powers of 1024. This causes confusion when your 1 TB hard drive shows as 931 GB in your operating system!
There are two systems for measuring file sizes: Decimal (SI) using powers of 1000, and Binary (IEC) using powers of 1024. This causes confusion when your 1 TB hard drive shows as 931 GB in your operating system!
Decimal System (SI)
Based on powers of 1000
Used by: Hard drive manufacturers, USB drives
- 1 KB = 1,000 bytes
- 1 MB = 1,000 KB = 1,000,000 bytes
- 1 GB = 1,000 MB = 1,000,000,000 bytes
- 1 TB = 1,000 GB = 1,000,000,000,000 bytes
Binary System (IEC)
Based on powers of 1024
Used by: Operating systems, RAM specifications
- 1 KiB = 1,024 bytes
- 1 MiB = 1,024 KiB = 1,048,576 bytes
- 1 GiB = 1,024 MiB = 1,073,741,824 bytes
- 1 TiB = 1,024 GiB = 1,099,511,627,776 bytes
Complete Size Conversion Table
| Unit | Symbol | Decimal (Base 1000) | Binary (Base 1024) | Bytes |
|---|---|---|---|---|
| Byte | B | 1 B | 1 B | 1 |
| Kilobyte / Kibibyte | KB / KiB | 1,000 B | 1,024 B | 1,000 / 1,024 |
| Megabyte / Mebibyte | MB / MiB | 1,000 KB | 1,024 KiB | 1,000,000 / 1,048,576 |
| Gigabyte / Gibibyte | GB / GiB | 1,000 MB | 1,024 MiB | 1,000,000,000 / 1,073,741,824 |
| Terabyte / Tebibyte | TB / TiB | 1,000 GB | 1,024 GiB | 1,000,000,000,000 / 1,099,511,627,776 |
| Petabyte / Pebibyte | PB / PiB | 1,000 TB | 1,024 TiB | 1,000,000,000,000,000 / 1,125,899,906,842,624 |
| Exabyte / Exbibyte | EB / EiB | 1,000 PB | 1,024 PiB | 1,000,000,000,000,000,000 / 1,152,921,504,606,846,976 |
Real-World Examples
Why Your 1 TB Drive Shows as 931 GB
Hard drive manufacturers use decimal (base 1000):
1 TB = 1,000,000,000,000 bytes
Your operating system uses binary (base 1024):
1,000,000,000,000 bytes รท 1,073,741,824 = 931.32 GiB
This is not a defect - it's just two different measurement systems!
RAM Always Uses Binary
When you buy 16 GB of RAM, you're actually getting:
16 GiB = 17,179,869,184 bytes = 17.18 GB (decimal)
RAM specifications always use the binary system because it matches how memory addressing works in computers.
Pro Tip:
When in doubt, use GiB, MiB, KiB for binary (1024-based) and GB, MB, KB for decimal (1000-based). The "i" in the middle stands for "binary" and eliminates confusion!
When in doubt, use GiB, MiB, KiB for binary (1024-based) and GB, MB, KB for decimal (1000-based). The "i" in the middle stands for "binary" and eliminates confusion!