There are 1,024 MB in a GB when storage is counted in binary units, which is what Windows, RAM makers and our data storage converter use. In the decimal system used by drive manufacturers and internet providers, there are 1,000 MB in a GB. Both conventions are in everyday use, and the gap between them is why a new 1 TB drive shows up as about 931 GB.
This guide explains bits and bytes, why there are two answers to "how many MB in a GB", and how to convert between KB, MB, GB, TB and PB without getting caught by the difference.
Bits and bytes
A bit is a single binary digit, a 0 or a 1. A byte is 8 bits, enough to store one basic text character. The symbols matter: a lowercase b means bits and an uppercase B means bytes. Internet speeds are quoted in bits per second (Mbps), while file sizes and storage are quoted in bytes (MB, GB), so the same number can differ by a factor of 8.
Decimal vs binary storage units
Computers address memory in powers of 2, so early on a "kilobyte" came to mean 1,024 bytes (2 to the power of 10) because it was close to 1,000. As capacities grew, the gap between powers of 1,000 and powers of 1,024 grew with them. Standards bodies introduced separate binary names (kibibyte, mebibyte, gibibyte, with symbols KiB, MiB, GiB), but many systems still write "KB", "MB" and "GB" for the binary values.
| Unit | Decimal (SI) size | Binary (IEC) size | Binary is larger by |
|---|---|---|---|
| Kilobyte | 1,000 bytes | 1,024 bytes (KiB) | 2.4% |
| Megabyte | 1,000,000 bytes | 1,048,576 bytes (MiB) | 4.9% |
| Gigabyte | 1,000,000,000 bytes | 1,073,741,824 bytes (GiB) | 7.4% |
| Terabyte | 1,000,000,000,000 bytes | 1,099,511,627,776 bytes (TiB) | about 10% |
| Petabyte | 1,000,000,000,000,000 bytes | 1,125,899,906,842,624 bytes (PiB) | 12.6% |
Who uses which:
- Binary: RAM sizes, Windows File Explorer, and many programming tools.
- Decimal: hard drive and SSD capacities, USB sticks, network speeds, and macOS file sizes.
Our converter uses binary units: 1 KB = 1,024 bytes, 1 MB = 1,024 KB, and so on up to PB. Its results match what Windows reports. If you need decimal figures, multiply or divide by 1,000 at each step instead.
Data storage conversion formulas
bytes = bits ÷ 8
binary: value in next unit up = value ÷ 1,024 (MB → GB, GB → TB)
decimal: value in next unit up = value ÷ 1,000
drive size in binary GB = advertised bytes ÷ 1,073,741,824Worked examples
Why a 1 TB drive shows 931 GB
- The manufacturer's 1 TB means 1,000,000,000,000 bytes (decimal).
- Windows divides by 1,073,741,824 bytes per binary gigabyte: 1,000,000,000,000 ÷ 1,073,741,824 = 931.32.
- So the drive appears as 931.32 GB. Nothing is missing; the same bytes are counted with a bigger unit.
A 2 TB drive works out to 1,862.65 GB the same way. The formatted drive will show slightly less again, because the file system reserves some space for its own records. To see the gap as a percentage, use the percentage calculator: 931.32 is 93.13% of 1,000. Our guide to the percentage calculator covers the method.
Internet speed vs download speed
A 100 Mbps connection moves 100,000,000 bits per second. Divide by 8 and you get 12,500,000 bytes per second, which is 12.5 MB/s in decimal units or 11.92 MB/s in binary units. That is the best case; real downloads run slower because of protocol overhead and network conditions.
Estimated download time is file size in bits divided by speed in bits per second. A 5 GB (decimal) file is 40,000 megabits, so at 100 Mbps it takes at least 400 seconds, or 6 minutes 40 seconds.
How much bigger Base64 makes a file
Base64 encoding turns every 3 bytes into 4 text characters, so encoded data is about 33% larger than the original. A 3 MB image becomes roughly 4 MB of Base64 text. You can see the growth by encoding a short text in the Base64 converter, and our article on Base64 use cases explains when the size cost is worth it.
How to use the Data Storage Converter
- Open the Data Storage Converter. It starts at 1 GB to MB, which shows 1,024.00.
- Enter the size in the Value field as a plain number, without thousands separators. Type 1000000000000, not 1,000,000,000,000.
- Choose the starting unit in the From list: Bits (b), Bytes (B), Kilobytes (KB), Megabytes (MB), Gigabytes (GB), Terabytes (TB) or Petabytes (PB).
- Choose the target unit in the To list.
- Read the Result. Values of 1 or more show two decimal places with thousands separators; values below 1 show eight decimal places, so 1 MB to GB reads 0.00097656.
- Use the swap button to reverse the conversion.
To check a drive's real capacity, enter the advertised size in bytes and convert to GB or TB. To compare an internet plan with a file size, enter the speed in bits and convert to MB.
Common data storage mistakes
- Confusing Mb with MB. Megabits and megabytes differ by a factor of 8. A 50 Mbps plan does not download 50 MB per second.
- Expecting a drive to show its advertised size. Decimal marketing and binary reporting guarantee a gap, and it grows from about 7% at GB scale to about 9% when the operating system reports in TB.
- Assuming one convention everywhere. RAM is binary, drives are decimal, and operating systems differ. Check which one a number uses before comparing.
- Typing commas into the value. The converter reads 1,000 as invalid input. Enter digits only.
Frequently asked questions
How many MB are in a GB?
There are 1,024 MB in a GB in binary units, used by Windows and for RAM. In decimal units, used by drive makers and network providers, there are 1,000 MB in a GB.
How many GB are in a TB?
A terabyte is 1,024 GB in binary units or 1,000 GB in decimal units. That is why a 1 TB drive appears as about 931 binary GB.
Why does my 1 TB hard drive only show 931 GB?
The manufacturer counts 1 TB as 1,000,000,000,000 bytes, while Windows divides by 1,073,741,824 bytes per GB. The result is 931.32 GB; no storage is missing, it is just measured in larger units.
How many bits are in a byte?
A byte is 8 bits. To convert a speed in megabits per second to megabytes per second, divide by 8.
What is the difference between Mbps and MB/s?
Mbps is megabits per second and is used for internet speeds; MB/s is megabytes per second and is used for file transfers. Since a byte is 8 bits, 100 Mbps equals 12.5 MB/s.
What is a gibibyte (GiB)?
A gibibyte is exactly 1,073,741,824 bytes (2 to the power of 30). It is the unambiguous name for the binary gigabyte that many systems still label as "GB".