When you need this conversion
Working out how many files fit: photos in a cloud plan, videos on a phone, attachments under a mailbox quota. Converting gigabytes to megabytes lets you compare against file sizes that are listed in MB.
Two meanings of “GB”
- Decimal GB = 1,000,000,000 bytes = 1,000 MB. Used on drive boxes, by macOS, iOS, Android and mobile carriers.
- Binary GiB = 1,073,741,824 bytes = 1,024 MiB. Windows uses this but labels it GB.
So a phone showing 64 GB and a PC showing 59.6 GB for the same storage are both right; they’re counting in different units.
Planning storage
- 1 GB ≈ 250 photos at 4 MB
- 1 GB ≈ 200 MP3 songs at 5 MB
- 1 GB ≈ 16 minutes of 1080p video at 8 Mbps
Common mistakes
Assuming the whole drive is usable. File systems and pre-installed software take space, so a 128 GB phone never offers all 128,000 MB.
Using 1,024 with decimal labels. 1.5 GB is 1,500 MB, not 1,536 MB.
For the reverse, use MB to GB.