Divide by 1,000 — or by 1,024
There are two answers because there are two standards. The decimal system (used by drive makers, networks and macOS) counts in powers of 1,000. The binary system (used by RAM and by Windows for file sizes) counts in powers of 1,024. Same word “gigabyte,” different size — and the gap grows at every level.
The gap between the two standards
A decimal gigabyte and a binary gigabyte drift apart by about 6.9% at this level. That is exactly why a drive sold as “1 TB” reads as roughly 931 GB in Windows.
A binary gigabyte holds about 7.4% more bytes than a decimal one. Nothing is lost on your drive — the maker's decimal bytes are simply relabelled with a smaller binary unit.
Common values
| MB | GB (decimal, ÷1000) | GiB (binary, ÷1024) |
|---|---|---|
| 100 MB | 0.1 GB | 0.0931 GiB |
| 500 MB | 0.5 GB | 0.4657 GiB |
| 1,000 MB | 1.0 GB | 0.9313 GiB |
| 1,024 MB | 1.024 GB | 1.0 GiB |
| 10,000 MB | 10.0 GB | 9.3132 GiB |
A stick sold as “16 GB” of RAM is really 16 GiB, which is about 17.2 decimal GB — the one place consumers see the binary count under a “GB” label.
Common questions
How many MB are in a GB?
In the decimal standard that drive makers and most software use, 1 GB is 1,000 MB. In the binary standard, 1 GiB is 1,024 MiB. Which one you want depends on the context, but 1,000 is the everyday answer.
Why does my 1 TB drive show up as about 931 GB?
The maker labels it in decimal units, so 1 TB means 1,000,000,000,000 bytes. Windows divides by 1,024 at each step but still writes "GB", so those bytes show as roughly 931. No space is missing; the two standards just count differently.
How do I convert MB to GB in my head?
For the decimal answer, move the decimal point three places left: 5,500 MB is 5.5 GB. If you need the binary value, dividing by 1,000 instead of 1,024 overshoots by only about 2.4%.
