Byte Storage Calculator
Convert any digital storage unit into any other — and understand why a "1 TB" drive shows up as 931 GB the moment you plug it in.
Formula
Decimal: 1 kB = 1,000 bytes · Binary: 1 KiB = 1,024 bytes
- Drive makers use decimal; operating systems often report binary
- The gap compounds, reaching about 9% by the terabyte
A 1 TB drive is 10¹² bytes, which Windows shows as 931 GiB
Two Competing Definitions
The confusion comes from two systems that use the same abbreviations:
- Decimal (SI): 1 kB = 1,000 bytes. Used by drive manufacturers.
- Binary (IEC): 1 KiB = 1,024 bytes. Used by operating systems.
The gap compounds at every step, which is why it grows with capacity.
Why Your Drive Looks Smaller
A manufacturer sells a drive as 1 TB meaning one trillion bytes. Windows divides by 1,024 three times and reports 931 GB.
Nothing is missing and nothing is faulty — the two are measuring the same bytes with different yardsticks. The shortfall is about 7% at gigabyte scale and roughly 10% at terabyte scale.
Bits Versus Bytes
Note the capital letter: B is a byte, b is a bit, and there are eight bits in a byte. Network speeds are quoted in bits per second while file sizes are in bytes, which is why a 100 Mbps connection transfers about 12.5 MB per second.
Quick Reference
| Advertised | Bytes | Shown as | Shortfall |
|---|---|---|---|
| 1 kB | 1,000 | 0.98 KiB | 2.3% |
| 1 MB | 10⁶ | 0.95 MiB | 4.6% |
| 1 GB | 10⁹ | 0.93 GiB | 6.9% |
| 1 TB | 10¹² | 931 GiB | 9.1% |
| 2 TB | 2 × 10¹² | 1.82 TiB | 9.1% |
Frequently Asked Questions
- Why does my 1 TB drive show as 931 GB?
- The manufacturer counts 1 TB as one trillion bytes, while your operating system divides by 1,024 at each step. Both describe the same bytes using different definitions.
- What is the difference between MB and MiB?
- A megabyte (MB) is 1,000,000 bytes; a mebibyte (MiB) is 1,048,576. The IEC introduced the binary names specifically to remove this ambiguity.
- How many MB are in a GB?
- 1,000 in decimal terms, or 1,024 in the binary sense your operating system uses.
- Why are download speeds in bits?
- Networking has measured throughput in bits per second since long before file sizes were commonly discussed in bytes, and the convention stuck.