Decimal vs binary units: why your 1 TB drive shows 931 GB
Storage makers use decimal (SI) units: 1 KB = 1,000 bytes, 1 MB = 1,000,000 bytes, 1 GB = 1,000,000,000 bytes. Windows and older software count in binary units of 1,024 but still label them KB, MB and GB. The correct binary names are KiB, MiB and GiB. That is why a 1 TB drive (10¹² bytes) appears as about 931 “GB” (931 GiB) in Windows.
- 1 GB = 1,000 MB (decimal); 1 GiB = 1,024 MiB (binary); 1 GB ≈ 0.931 GiB.
- Bits and bytes: 1 byte = 8 bits. Internet speeds are in megabits per second (Mbps), so a 100 Mbps connection downloads about 12.5 MB per second.
Common data storage conversion factors
| Unit | Equals | Reverse |
|---|---|---|
| 1 gigabyte | 1,000 MB | 1 megabyte = 0.001 GB |
| 1 megabyte | 1,000 KB | 1 kilobyte = 0.001 MB |
| 1 terabyte | 1,000 GB | 1 gigabyte = 0.001 TB |
| 1 gigabyte | 0.9313225746 GiB | 1 gibibyte = 1.073741824 GB |
| 1 megabit | 0.125 MB | 1 megabyte = 8 Mb |
| 1 kilobyte | 1,000 B | 1 byte = 0.001 KB |
| 1 petabyte | 1,000 TB | 1 terabyte = 0.001 PB |
| 1 gibibyte | 1,024 MiB | 1 mebibyte = 0.0009765625 GiB |
| 1 terabyte | 0.9094947018 TiB | 1 tebibyte = 1.099511628 TB |
| 1 byte | 8 b | 1 bit = 0.125 B |
Data storage conversions
Each of these has its own page with the formula, worked examples and a full conversion table:
All data storage units on this converter
| Unit | Symbol | 1 unit equals | System |
|---|---|---|---|
| Bit | b | 0.125 B | Bits |
| Kilobit | kb | 125 B | Bits |
| Megabit | Mb | 1,25,000 B | Bits |
| Gigabit | Gb | 12,50,00,000 B | Bits |
| Terabit | Tb | 1,25,00,00,00,000 B | Bits |
| Byte | B | 1 B | Decimal (SI, 1000) |
| Kilobyte | KB | 1,000 B | Decimal (SI, 1000) |
| Megabyte | MB | 10,00,000 B | Decimal (SI, 1000) |
| Gigabyte | GB | 1,00,00,00,000 B | Decimal (SI, 1000) |
| Terabyte | TB | 10,00,00,00,00,000 B | Decimal (SI, 1000) |
| Petabyte | PB | 1 × 10¹⁵ B | Decimal (SI, 1000) |
| Kibibyte | KiB | 1,024 B | Binary (IEC, 1024) |
| Mebibyte | MiB | 10,48,576 B | Binary (IEC, 1024) |
| Gibibyte | GiB | 1,07,37,41,824 B | Binary (IEC, 1024) |
| Tebibyte | TiB | 10,99,51,16,28,000 B | Binary (IEC, 1024) |
| Pebibyte | PiB | 1.1258999 × 10¹⁵ B | Binary (IEC, 1024) |
Frequently asked questions
Is 1 GB 1000 MB or 1024 MB?
Officially (SI) 1 GB = 1,000 MB. In binary units 1 GiB = 1,024 MiB, which Windows displays as “GB”. This converter offers both.
How many MB are in 1 Mb?
1 megabit (Mb) = 0.125 megabytes (MB), because a byte is 8 bits. Lower-case b means bits.
Why does my 1 TB hard drive show 931 GB?
The drive has 1,000,000,000,000 bytes. Windows divides by 1,024³ and shows 931 “GB”, which are really GiB. No space is missing.