Data size converter: MB, GB, TB and the 1000 vs 1024 question
Type in either box to convert between bits, bytes, KB, MB, GB and TB. Decimal and binary results show together.
The short answer
1 GB is 1,000 MB in the decimal units drive makers use, while 1 GiB is 1,024 MiB in binary units. A 1 TB drive holds 10¹² bytes, which is 931.32 GiB, so a computer that counts in 1,024s reports it as about 931 GB. Nothing is missing; the two numbers measure the same bytes.
How it is calculated
1 byte = 8 bits
Decimal: 1 KB = 1,000 B; 1 MB = 1,000 KB; 1 GB = 1,000 MB; 1 TB = 1,000 GB
Binary: 1 KiB = 1,024 B; 1 MiB = 1,024 KiB; 1 GiB = 1,024 MiB; 1 TiB = 1,024 GiB
Worked example
You plug in a new external drive sold as 1 TB, and your computer reports roughly 931 GB.
- Advertised: 1 TB = 1,000⁴ = 1,000,000,000,000 bytes
- One GiB = 1,024³ = 1,073,741,824 bytes
- 1,000,000,000,000 ÷ 1,073,741,824 = 931.32 GiB
The drive is a full 1 TB; 931.32 is the same capacity counted in binary units and labeled "GB"
Quick reference table
| Advertised | Bytes | Shown (GiB) | In TiB |
|---|---|---|---|
| 128 GB | 128,000,000,000 | 119.21 GiB | 0.116 TiB |
| 256 GB | 256,000,000,000 | 238.42 GiB | 0.233 TiB |
| 512 GB | 512,000,000,000 | 476.84 GiB | 0.466 TiB |
| 1 TB | 1,000,000,000,000 | 931.32 GiB | 0.909 TiB |
| 2 TB | 2,000,000,000,000 | 1,862.65 GiB | 1.819 TiB |
| 4 TB | 4,000,000,000,000 | 3,725.29 GiB | 3.638 TiB |
Special cases and common mistakes
- The gap grows with each prefix. Decimal vs binary is 2.34% at kilo, 6.87% at giga and 9.05% at tera, which is why the difference is easy to miss on a USB stick and obvious on a hard drive.
- Mbps is not MB/s. Internet plans are sold in megabits per second; file sizes are in megabytes. Divide by 8: a 300 Mbps plan downloads at most 37.5 MB/s.
- KiB, MiB and GiB are official names. The IEC approved the binary prefixes kibi, mebi and gibi in 1998 so that kilo and mega would always mean 1,000 and 1,000,000. NIST publishes the same table.
Frequently asked questions
How many MB are in a GB?
1,000 MB in decimal units, the ones on product boxes. In binary units, 1 GiB is 1,024 MiB.
Is 1 GB 1000 or 1024 MB?
Officially 1,000. The 1,024 value belongs to the gibibyte (GiB), though some operating systems still label binary values as "GB".
Why does my 1 TB drive only show 931 GB?
Because 1 TB is 10¹² bytes, and dividing by 1,024³ gives 931.32. The capacity is the same; only the unit changes.
How many GB is 128 GB in GiB?
119.21 GiB. That is why a 128 GB phone or SSD shows less space before any apps are installed.
How many KB are in an MB?
1,000 KB in a megabyte, or 1,024 KiB in a mebibyte.
How do I convert Mbps to MB/s?
Divide by 8. 100 Mbps is 12.5 MB/s and 1 Gbps is 125 MB/s.
Sources
- NIST: Prefixes for binary multiples (IEC kibi, mebi, gibi; approved December 1998) (Last reviewed: October 9, 2026)