GB vs GiB, MB vs MiB: Digital Storage Units Explained
Buy a "1 TB" drive, plug it in, and your computer says 931 GB. Did you get ripped off? No — you've hit the decimal-vs-binary units confusion. Here's the clear explanation.
Two different systems
There are two ways to count digital storage:
- Decimal (SI): 1 kB = 1,000 bytes, 1 MB = 1,000,000 bytes, and so on — powers of 1,000. Drive makers use this.
- Binary (IEC): 1 KiB = 1,024 bytes, 1 MiB = 1,048,576 bytes — powers of 1,024. Operating systems often use this but label it "GB".
Why "1 TB" shows as 931 GB
The drive holds 1,000,000,000,000 bytes (1 decimal TB). Your OS divides by 1,024 three times to get "GB" (really GiB), giving ≈ 931. Same bytes, different yardstick. Nothing is missing.
The proper names
| Decimal | Bytes | Binary | Bytes |
|---|---|---|---|
| 1 KB | 1,000 | 1 KiB | 1,024 |
| 1 MB | 1,000,000 | 1 MiB | 1,048,576 |
| 1 GB | 1,000,000,000 | 1 GiB | 1,073,741,824 |
| 1 TB | 10¹² | 1 TiB | 1,099,511,627,776 |
The gap grows with size: ~2.4% at GB, ~10% at TB. That's why big drives "lose" more.
Bits vs bytes (another gotcha)
Internet speeds are measured in bits per second (Mbps), but file sizes in bytes (MB). There are 8 bits in a byte, so a "100 Mbps" connection downloads at about 12.5 MB/s at best. Divide Mbps by 8 to estimate MB/s.
Convert instantly
Our unit converter supports both decimal (KB/MB/GB/TB) and binary (KiB/MiB/GiB/TiB) units, plus bits — so you can move between them without doing the powers-of-1,024 math yourself.
FAQ
Is my drive smaller than advertised?
No. It has exactly the advertised number of bytes; your OS just displays them using binary units labeled "GB".
Should I use GB or GiB?
Use GiB/MiB when you mean binary (powers of 1,024) to avoid ambiguity; use GB/MB for decimal.
Why is my download slower than my plan?
Plans are in megabits; files are in megabytes. Divide your Mbps by 8 for the real MB/s.