Convert between bytes, KB, MB, GB and TB instantly.
This converts between bytes, kilobytes, megabytes, gigabytes and terabytes — and, importantly, between the two competing definitions of those words. Digital storage is the one area where the same unit name genuinely means two different quantities depending on who is using it, and that ambiguity is why your new drive appears smaller than advertised.
Computers address memory in powers of two, so 2^10 = 1,024 became the natural "thousand" in early computing and the SI prefixes were borrowed loosely to describe it. Storage manufacturers, meanwhile, use the SI prefixes literally: a kilobyte is 1,000 bytes.
| Unit | Decimal (SI) | Binary unit | Binary value | Gap |
|---|---|---|---|---|
| Kilobyte | 1,000 B | Kibibyte (KiB) | 1,024 B | 2.4% |
| Megabyte | 1,000,000 B | Mebibyte (MiB) | 1,048,576 B | 4.9% |
| Gigabyte | 10^9 B | Gibibyte (GiB) | 1,073,741,824 B | 7.4% |
| Terabyte | 10^12 B | Tebibyte (TiB) | 1,099,511,627,776 B | 10.0% |
| Petabyte | 10^15 B | Pebibyte (PiB) | 2^50 B | 12.6% |
Notice the gap widens at every step. At kilobyte scale it is a rounding error; at terabyte scale it is a tenth of your drive.
This is the single most common storage question, and nobody is cheating you. The manufacturer sells a drive holding 1,000,000,000,000 bytes and correctly labels it 1 TB using SI prefixes. Windows then reports capacity in binary units but labels them with the decimal names, dividing by 1,073,741,824 and printing "GB":
So the drive holds exactly what was advertised; Windows is displaying gibibytes while calling them gigabytes. macOS and most Linux distributions switched to true decimal reporting years ago, which is why the same drive reads as 1 TB on a Mac and 931 GB on a PC. A few gigabytes of formatting overhead and file system structures account for a further small difference.
A byte is eight bits, and the distinction matters most for network speeds. Internet connections are advertised in megabits per second (Mbps, lowercase b), while download managers report megabytes per second (MB/s, capital B). Divide by eight to get from one to the other.
A 100 Mbps connection downloading a 5 GB file therefore takes at least 400 seconds, not 50. Real throughput runs lower still — protocol overhead, latency and contention typically cost 10-20%.
| Content | Typical size |
|---|---|
| Plain text page | 2-4 KB |
| Smartphone photo (12 MP JPEG) | 3-5 MB |
| RAW photo | 25-50 MB |
| MP3 song, 3 minutes | 3-5 MB |
| Hour of 1080p video | 2-4 GB |
| Hour of 4K video | 15-25 GB |
| Modern AAA game | 50-150 GB |
These make capacity planning tractable: a 1 TB drive holds roughly 200,000 phone photos, or about 40 hours of 4K footage, or a dozen large games.
Beyond the prefix issue, several things consume space before you store anything. The file system itself takes a small percentage for metadata and allocation tables. Block size means every file occupies a whole number of clusters, so a 1 KB file on a 4 KB cluster wastes 3 KB — negligible individually, significant across hundreds of thousands of small files. SSDs reserve a portion for wear levelling and spare blocks, and they need free space to maintain write performance, so filling one past about 90% degrades speed noticeably. Solid-state drives should be left with meaningful headroom rather than filled to the last gigabyte.
The manufacturer counts 1 TB as 1,000,000,000,000 bytes using SI prefixes. Windows divides by 1,073,741,824 — the binary gibibyte — but still writes "GB", giving 931. The drive holds exactly what was advertised; the two systems are using the same word for different quantities.
A megabyte (MB) is 1,000,000 bytes under the SI definition. A mebibyte (MiB) is 1,048,576 bytes, or 2^20. The MiB naming was introduced by the IEC in 1998 specifically to remove the ambiguity, though adoption has been patchy.
Connection speeds are quoted in megabits per second and download managers report megabytes per second — a factor of eight. A 100 Mbps line maxes out at 12.5 MB/s, and protocol overhead and contention typically take another 10-20% off that.
Roughly 200,000 typical smartphone JPEGs at 4-5 MB each, or about 25,000 RAW files. For video, expect around 40 hours of 4K or 300 hours of 1080p depending on the encoder and bitrate.
No. SSDs need free blocks for wear levelling and garbage collection, and write performance falls off noticeably above roughly 90% capacity. Leaving 10-15% free is sensible practice.