How to use
- Type a number in Value.
- Pick the From and To units. Decimal (MB, GB) and binary (MiB, GiB) units are grouped separately.
- Read the answer. Use bits (Mbit) for internet speeds.
How the conversion works
There are two systems. Decimal (SI) prefixes step by 1,000. Binary (IEC) prefixes step by 1,024:
| Prefix | Decimal (SI) | Binary (IEC) |
|---|---|---|
| kilo / kibi | 1,000 B | 1,024 B |
| mega / mebi | 1,000,000 B | 1,048,576 B |
| giga / gibi | 1,000,000,000 B | 1,073,741,824 B |
| tera / tebi | 1,000,000,000,000 B | 1,099,511,627,776 B |
One byte (B) is 8 bits (b). The converter goes through bytes, so every result is exact before rounding.
Examples
- 4,500 MB to GB: 4,500 ÷ 1,000 = 4.5 GB
- A 1 TB drive in binary units: 10¹² ÷ 1,024³ = 931.32 GiB
- 100 Mbit to MB: 100 ÷ 8 = 12.5 MB
Conversion charts
Why your drive looks smaller
| Advertised size | Bytes | In binary units |
|---|---|---|
| 128 GB | 128,000,000,000 | 119.2 GiB |
| 256 GB | 256,000,000,000 | 238.4 GiB |
| 512 GB | 512,000,000,000 | 476.8 GiB |
| 1 TB | 1,000,000,000,000 | 931.3 GiB |
| 2 TB | 2,000,000,000,000 | 1.82 TiB |
| 4 TB | 4,000,000,000,000 | 3.64 TiB |
Drive makers count in powers of 1,000. Windows divides by 1,024 but still writes “GB”, so a 1 TB drive shows as about 931 GB. No space is missing.
Bits to bytes
| Megabits (Mbit) | Megabytes (MB) |
|---|---|
| 10 | 1.25 |
| 25 | 3.125 |
| 50 | 6.25 |
| 100 | 12.5 |
| 300 | 37.5 |
| 500 | 62.5 |
| 1,000 | 125 |
The same ratio applies per second: a 100 Mbps connection moves at most 12.5 MB of data each second.
More detail: who uses which system
- SI prefixes (kilo, mega, giga) mean powers of 10 by definition. The BIPM says they must not be used for powers of 2.
- IEC prefixes (kibi, mebi, gibi) were approved in December 1998 for powers of 2.
- Windows reports binary values with “KB”, “MB” and “GB” labels.
- Apple says it used binary reporting up to iOS 10 and OS X Leopard.
- Formatted capacity is also a little lower because the file system reserves space.
Need the gap as a percentage? The percentage calculator shows it.