GB to MB Converter
Enter a number of gigabytes and the megabyte figure follows as you type. Multiply by 1,024 by default, or tick the SI box to multiply by 1,000.
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Created by the Reeliy Editorial Team. Last updated: Oct 19, 2026
How many megabytes are in a gigabyte?
That depends on which system of prefixes you follow. In the binary convention used by memory and by Windows, a gigabyte contains 1,024 megabytes. Under SI, where giga means a billion and mega a million, a gigabyte contains exactly 1,000 megabytes.
binary: MB = GB × 1,024
SI: MB = GB × 1,000
The converter starts in binary mode. Tick Use SI standard to switch; the result is recalculated from the number already typed in, so you can flip between the two and compare.
Difference between GB and MB
Both are units of digital information, a thousand-fold (or 1,024-fold) apart. Megabytes suit individual files such as documents, photographs and songs. Gigabytes suit collections and devices: a film, a phone's memory, a game install or a monthly mobile data allowance.
The binary names for these sizes are gibibyte (GiB) and mebibyte (MiB), with 1 GiB = 1,024 MiB. Software seldom uses them, so the plain labels GB and MB end up carrying both meanings. When precision matters, check which convention a document or program is using before comparing figures.
How to convert GB to MB
- Type the size in gigabytes.
- Choose binary (default) or SI by leaving the checkbox clear or ticking it.
- Read the megabytes in the second box.
Decimals work, and results are rounded to four decimal places with no thousands separators. If the first box is emptied the previous answer stays on screen.
Example: a 4.7 GB disc
A single-layer DVD is sold as 4.7 GB, a decimal figure. In SI terms that is 4.7 × 1,000 = 4,700 MB. Counted the binary way, the same number multiplied by 1,024 gives 4.7 × 1,024 = 4,812.8 MB, which is why a disc can appear to hold less than its label suggests when a system reports in binary units.
GB to MB conversion table
| Gigabytes (GB) | MB, binary (× 1,024) | MB, SI (× 1,000) |
|---|---|---|
| 0.25 | 256 | 250 |
| 0.5 | 512 | 500 |
| 1 | 1,024 | 1,000 |
| 2 | 2,048 | 2,000 |
| 4 | 4,096 | 4,000 |
| 5 | 5,120 | 5,000 |
| 8 | 8,192 | 8,000 |
| 10 | 10,240 | 10,000 |
| 16 | 16,384 | 16,000 |
| 32 | 32,768 | 32,000 |
| 64 | 65,536 | 64,000 |
| 100 | 102,400 | 100,000 |
Neighbouring conversions: MB to GB for the reverse, and GB to TB for the next unit up.
Common mistakes
- Using the wrong convention for the job. Memory modules are built in powers of two, so an 8 GB module holds 8,192 MB, while a phone plan or a drive label is normally decimal, where 8 GB is 8,000 MB.
- Confusing GB with Gb. A lowercase b is a bit; 8 Gb is a single gigabyte (8 ÷ 8) of data.
- Comparing a binary figure with a decimal one. Subtracting 2,000 MB (SI) of usage from 3 GB counted as 3,072 MB (binary) leaves an answer that is neither convention. Pick one for the whole calculation.
Frequently asked questions
How many MB are in 1 GB?
1 GB is 1,024 MB in the binary convention and 1,000 MB in the SI convention.
How do I convert GB to MB?
Multiply the gigabytes by 1,024 for binary or by 1,000 for SI. For example, 3 GB is 3,072 MB in binary and 3,000 MB in SI.
Which should I use, 1,024 or 1,000?
Use 1,000 when you are working from manufacturer specifications or network data allowances, which follow SI. Use 1,024 when matching what many operating systems and memory sizes report.
What is the difference between GB and GiB?
GB usually means 1,000,000,000 bytes, while GiB means exactly 1,073,741,824 bytes (1,024 × 1,024 × 1,024). Many programs print GB when they really mean GiB.
References
Cite this converter and page
If you use this page in your work, you can cite it as:
Reeliy Editorial Team. (2026). GB to MB Converter. Reeliy. https://reeliy.com/converters/convert-gb-to-mb“GB to MB Converter.” Reeliy, 2026, https://reeliy.com/converters/convert-gb-to-mb.