GB to MB Converter — Gigabytes to Megabytes (1024 & 1000)
A GB to MB converter turns gigabytes into megabytes — the conversion people need when a download, a partition or a data plan is quoted in one unit and their tool shows the other.
Quick answer: With the binary rule used by Windows and most software, 1 GB = 1,024 MB. With the decimal rule used by drive, phone and cloud vendors, 1 GB = 1,000 MB. The binary value is 2.4% larger, which is why both numbers can honestly describe the same file.
The two lines are the same file — only the definition of “GB” differs. This 2.4% gap per step is why a 1 TB drive shows 931 GiB in Windows.
| GB | MB |
|---|---|
| 0.5 | 512 |
| 1 | 1,024 |
| 2 | 2,048 |
| 5 | 5,120 |
| 10 | 10,240 |
| 50 | 51,200 |
| 100 | 102,400 |
| 500 | 512,000 |
| 1,000 | 1,024,000 |
| 1 GB (binary) | 1,024 MB = 1,073,741,824 bytes |
|---|---|
| 1 GB (decimal) | 1,000 MB = 1,000,000,000 bytes |
| Difference | 6.87% more bytes in the binary GB (1.024³) |
| Unit symbols | GB (decimal or binary, ambiguous) · GiB (always 1024³) |
| Common use | Data plans, disk partitions, download sizes, cloud quotas |
Why GB to MB has two right answers
A gigabyte began as a power of ten — 1,000 megabytes — because SI prefixes are decimal. Computer memory, however, is addressed in powers of two, so software has always counted 1,024. In 1998 the IEC introduced GiB/MiB/KiB for the 1024 version, but two decades later Windows still labels binary quantities as “GB”, phone vendors label decimal ones as “GB”, and both are technically allowed. When someone asks how many MB are in a GB, the honest answer includes the rule being used.
Where the difference bites hardest
Dividing and multiplying repeats the 2.4% error at every step: one step is 2.4%, three steps (GB → MB → bytes in a compressed pipeline) reaches about 7%. That is exactly the gap between a 1 TB drive label and the 931 GiB Windows reports: 1,000 GB × 1.024³ versus 1,000 GiB. It also explains why a “50 GB” game download can need 53 GB of disk space once the launcher counts in binary.
Which number should you use?
For anything your operating system will display — free space, partition sizes, file properties — use 1,024 so your arithmetic matches the screen. For anything a vendor quotes — mobile data, cloud plans, drive capacity, upload limits — use 1,000 and expect the system to show a slightly smaller figure afterwards. When in doubt, convert to bytes: 1 GB = 10⁹ or 2³⁰ bytes, and no label can argue with that.
When to use this calculator
- Checking whether a 25 GB game fits in the free space Windows reports in GB.
- Translating a mobile data plan (decimal GB) into what your phone's usage meter shows.
- Sizing partitions or virtual machine disks where the tool asks for MB.
- Sanity-checking cloud storage quotas before a backup runs.
- Working out how many 700 MB CD images fit on a DVD or drive.