What this tool does
There are two defensible answers to how many megabytes are in a gigabyte, and they differ by about 7%. Storage makers use the decimal system, where a kilobyte is 1,000 bytes, while operating systems count in steps of 1,024 and still print the same three-letter abbreviations. This converter shows both definitions at once, so a file size, a disk capacity and a network speed can be compared without guessing where the number came from.
How it works
A byte is eight bits, and that relationship never changes — it is the foundation of every unit above it. Two ladders then sit on top. The SI decimal ladder multiplies by 1,000: 1 kB = 1,000 bytes, 1 MB = 10^6 bytes, 1 GB = 10^9 bytes, 1 TB = 10^12 bytes. Drive makers and network speeds use it because the numbers stay round.
The IEC binary ladder multiplies by 1,024 and uses different suffixes: 1 KiB = 1,024 bytes, 1 MiB = 1,048,576 bytes, 1 GiB = 1,073,741,824 bytes. Windows and macOS still report these binary steps under the labels KB, MB and GB, which is why a drive sold as 1 TB shows about 931 GB: 10^12 divided by 1,073,741,824 is 931.32.
To move between the systems, always go through bytes. Multiply the source unit by its byte value, then divide by the target unit's byte value. One megabyte is 1,000,000 bytes and one mebibyte is 1,048,576, so 1 MB = 0.9537 MiB. Converting MB to GB with 1,000 and with 1,024 gives different results, and neither is wrong — it depends on which definition the figure was written under.
Worked example
Explaining why a 1 TB drive shows 931 GB, and converting 1 GB to MB.
- 1 TB = 10^12 bytes under the decimal SI definition
- 10^12 ÷ 1,073,741,824 = 931.32 GiB
- 1 GB = 10^9 bytes ÷ 10^6 = 1,000 MB, or ÷ 2^20 = 953.67 MiB
A 1 TB drive holds 931.32 GiB, which Windows labels 931 GB. One decimal GB is 1,000 MB but only 953.67 MiB.
Accuracy and limitations
- Operating systems display binary steps with decimal labels, so this tool reports both definitions side by side instead of pretending only one exists.
- Formatting, filesystem metadata and the decimal units used by manufacturers mean usable capacity is always slightly below the figure on the box.
- Network rates are decimal by convention, so 100 Mbps is 100,000,000 bits per second or 12.5 MB per second, not 100 MB per second.
Frequently asked questions
- Why does my 1TB drive show 931 GB?
- Because the drive is 10^12 bytes and Windows counts a gigabyte as 1,073,741,824 bytes; the division gives 931.32. Nothing is missing — the two systems simply define a gigabyte differently.
- How many MB are in a GB?
- 1,000 MB if both are decimal SI units, or 1,024 MB if both are the binary units Windows reports. Either way the bytes are the same: 1 GB = 1,000,000,000 bytes = 953.67 MiB.
- How many bytes are in a megabyte?
- 1,000,000 bytes in a decimal MB, and 1,048,576 bytes in a binary MiB. The gap compounds at scale, which is why 1 TB works out to 931.32 GiB rather than 1,000.
- How many bits are in a byte?
- Eight, always. That matters because network speeds are quoted in bits: 100 Mbps is 12.5 megabytes per second of transfer, not 100.
- What is the difference between KB and KiB?
- KB is 1,000 bytes under the SI definition and KiB is 1,024 bytes under the IEC one. The IEC suffixes exist so binary sizes can be told apart from decimal ones at a glance.
- How do I convert GB to TB?
- Divide by 1,000 for the decimal units used by drive makers, or by 1,024 for the binary units an operating system reports. In binary terms 1 TiB is 1,024 GiB.