Decimal (1000) vs binary (1024)
There are two answers to "how many MB are in a GB", and both are in everyday use. Which one you need depends on where your number came from.
- Decimal, 1,000 per step. Each unit is 1,000 times the one below. This is the SI standard, and what drive manufacturers, internet providers and most published specifications mean.
- Binary, 1,024 per step. Each unit is 1,024 times the one below. The standardized binary names are KiB, MiB, GiB, TiB and PiB.
The difference grows with each step: 1 kB is 1,000 bytes while 1 KiB is 1,024 bytes. By the time you reach the tera level, the corresponding binary unit contains about 10% more bytes than the decimal unit.
| Unit | Decimal (bytes) | Binary (bytes) | Difference |
|---|---|---|---|
| KB | 1,000 | 1,024 | 2.4% |
| MB | 1,000,000 | 1,048,576 | 4.9% |
| GB | 1,000,000,000 | 1,073,741,824 | 7.4% |
| TB | 1,000,000,000,000 | 1,099,511,627,776 | 10.0% |
| PB | 1,000,000,000,000,000 | 1,125,899,906,842,624 | 12.6% |
Why your 1 TB drive shows up as 931 GB
The manufacturer sold you 1,000,000,000,000 bytes and called that 1 TB, using decimal units. If the same bytes are divided by 1,024³, the result is about 931.32 GiB. Some software may display that binary quantity using the label "GB", which is one reason the terminology causes confusion.
Both numbers describe the same drive. The only thing that changed is what the label means. Formatting does consume a little genuine space for the filesystem, but that's a fraction of a percent, not the 7% gap you see here.
KiB, MiB and GiB: the unambiguous names
The IEC introduced separate names for the binary units precisely to end this confusion. A kibibyte (KiB) is 1,024 bytes, a mebibyte (MiB) is 1,048,576 bytes, and a gibibyte (GiB) is 1,073,741,824 bytes. Under the SI/IEC terminology, kB, MB and GB are decimal units, while KiB, MiB and GiB are binary units.
| Decimal name | Value | Binary name | Value |
|---|---|---|---|
| Kilobyte (kB) | 1,000¹ bytes | Kibibyte (KiB) | 1,024¹ bytes |
| Megabyte (MB) | 1,000² bytes | Mebibyte (MiB) | 1,024² bytes |
| Gigabyte (GB) | 1,000³ bytes | Gibibyte (GiB) | 1,024³ bytes |
| Terabyte (TB) | 1,000⁴ bytes | Tebibyte (TiB) | 1,024⁴ bytes |
| Petabyte (PB) | 1,000⁵ bytes | Pebibyte (PiB) | 1,024⁵ bytes |
The binary names are especially useful in technical contexts because they remove the ambiguity between powers of 1,000 and powers of 1,024. Most software still writes "GB" while meaning GiB, which is why this converter asks which one you mean rather than guessing.
Common conversions
| Conversion | Decimal | Binary |
|---|---|---|
| Bytes to kilobyte | ÷ 1,000 | ÷ 1,024 |
| Kilobyte to megabyte | ÷ 1,000 | ÷ 1,024 |
| Megabyte to gigabyte | ÷ 1,000 | ÷ 1,024 |
| Gigabyte to terabyte | ÷ 1,000 | ÷ 1,024 |
| Megabyte to kilobyte | × 1,000 | × 1,024 |
| Gigabyte to megabyte | × 1,000 | × 1,024 |
| Terabyte to gigabyte | × 1,000 | × 1,024 |
Bits and bytes are not the same unit
A byte is 8 bits, and the capital letter matters: MB means megabytes, Mb means megabits. Storage is quoted in bytes; network and internet speeds are quoted in bits per second. You can use the Data Transfer Converter to convert between common data-rate units. A 100 Mbps connection has a theoretical data rate of about 12.5 MB/s before protocol and other overhead. This converter works entirely in bytes.
If you know the size of a file and your connection speed, you can also estimate how long a transfer will take with our Download Time Calculator.
Frequently asked questions
How many MB are in a GB?
1,000 in decimal units, or 1,024 in binary units. If the figure came from a drive box, a spec sheet or an internet plan, use 1,000. If it came from your operating system's file browser or disk properties, use 1,024.
Why does my 1 TB drive show 931 GB?
Because the manufacturer counted in decimal units and your computer counts in binary ones. 1,000,000,000,000 bytes divided by 1,024 three times is 931.32, and your system labels that "GB" when it strictly means GiB. No storage is missing — the two numbers describe the same drive.
Which convention should I use?
Hardware specifications and storage manufacturers commonly use decimal units. Some operating systems and software display quantities using binary multiples, sometimes while retaining familiar labels such as GB. When precision matters, use kB/MB/GB for decimal units and KiB/MiB/GiB for binary units.
Is RAM measured in decimal or binary?
RAM capacities are commonly based on powers of two. For example, a memory capacity corresponding to 8 GiB is 8 × 1,024³ bytes. Memory specifications may still use labels such as GB, so the unit label alone does not always tell you which convention is being used.
What's the difference between MB and Mb?
MB is megabytes, Mb is megabits, and a byte is 8 bits. Storage uses bytes; connection speeds use bits per second. A 100 Mbps line moves about 12.5 MB each second.