Why a "1 TB" drive shows up as 931 GB
Digital storage is the rare unit system where the marketing label and the measurement are two different things. A drive sold as "1 TB" reports 931 GB on your computer — not because it's defective, but because manufacturers count in decimal (1,000 = 1 kilo) while operating systems count in binary (1,024 = 1 kilo). This page explains that gap, the bit-versus-byte difference behind your real download speed, and how the units stack up from a single bit to a petabyte. The tool above converts between all of them in both scales.
The bit-versus-byte trap that decides your download speed
Your internet plan is sold in megabits per second (Mbps), but download managers and browsers show progress in megabytes per second (MB/s). The two are separated by a factor of exactly 8 — one byte is 8 bits. So a 100 Mbps fibre plan can deliver at most 100 ÷ 8 = 12.5 MB/s. When a 5 GB game shows an estimated download time, the app has already done this division for you. If a speed test reports 94 Mbps, your real file-download rate is about 11.75 MB/s — the same number the Data tool returns when you convert 94 megabits to megabytes.
Binary vs decimal: who counts which way
- Decimal (base 10, used by manufacturers): 1 KB = 1,000 bytes, 1 MB = 1,000,000 bytes, 1 GB = 1,000,000,000 bytes. This is how storage capacity is advertised on boxes.
- Binary (base 2, used by operating systems): 1 KiB = 1,024 bytes, 1 MiB = 1,048,576 bytes, 1 GiB = 1,073,741,824 bytes. Windows and macOS report in these, though they still label them "KB", "MB" and "GB".
The result: a "500 GB" drive is 500,000,000,000 bytes = 465.66 GiB, which Windows displays as "465 GB". Neither party is wrong; they are using different reference points. That 931 GB "missing" from a 1 TB drive is the same phenomenon at a bigger scale.
The digital hierarchy, bit to petabyte
| Unit | Abbreviation | Binary Equivalent | Real-World Example |
|---|---|---|---|
| Bit | b | Smallest unit (1 or 0) | A single binary signal |
| Byte | B | 8 bits | One letter of text |
| Kilobyte | KB | 1,024 bytes | A short email |
| Megabyte | MB | 1,024 KB | A high-quality MP3 (~4 MB) |
| Gigabyte | GB | 1,024 MB | An HD movie (~3–5 GB) |
| Terabyte | TB | 1,024 GB | A modern gaming console drive |
| Petabyte | PB | 1,024 TB | Large cloud data centres |
How much actually fits where
Real-world estimates vary with quality, but these are useful planning numbers:
- A 12-megapixel phone photo is roughly 3–4 MB, so 1 GB holds about 250–300 photos.
- A 4K (not compressed) minute of video runs about 375 MB — a 1 TB drive fits roughly 45 hours.
- A typical song is 3–5 MB in MP3, so 1 GB is about 250 songs.
- Text is tiny: a 100-page novel is around 300–400 KB, meaning a 4 GB flash drive holds thousands of them.
Data unit questions that keep coming up
Is my 1 TB drive actually faulty?
Almost certainly not. Check the decimal-vs-binary gap above: 1 TB advertised = 1,000,000,000,000 bytes = 931.32 GiB. A drive reporting 931 GB in Windows is behaving exactly as designed.
Why do I need to divide Mbps by 8?
Because "Mbps" is megabits and "MB/s" is megabytes, and there are 8 bits in every byte. Divide any Mbps figure by 8 to get the theoretical maximum MB/s — real-world speeds are lower due to overhead, so treat it as a ceiling.
What comes after a petabyte?
In order: exabyte (1,024 PB), zettabyte (1,024 EB), then yottabyte (1,024 ZB). Internet providers and big-tech clouds are the only organisations dealing in these today.
Is a kibibyte the same as a kilobyte?
Not exactly. A kilobyte (KB) is 1,000 bytes; a kibibyte (KiB) is 1,024 bytes. The binary names (–bi–) exist precisely to remove this ambiguity — this tool converts in both scales so you can pick whichever your software reports.