KB vs KiB, MB vs MiB: Why 1 TB Shows 931 GB (Free)
A KB is 1,000 bytes and a KiB is 1,024. That's why a 1 TB drive shows 931 GB and a "50 KB" limit can trip you up. Convert with a free unit converter.
Published · 5 min read
A kilobyte (KB) is 1,000 bytes and a kibibyte (KiB) is 1,024 bytes. The same split runs all the way up: a megabyte (MB) is 1,000,000 bytes, a mebibyte (MiB) is 1,048,576. Drive makers count in thousands, while Windows counts in 1,024s but still writes "GB", so a 1 TB drive shows up as about 931 GB. The free unit converter has both kinds under Data size, so you can check any figure in a second.
Nothing is missing from your drive, and nobody is cheating you. Two counting systems share almost the same names, and that causes real confusion, especially when an online form says "maximum 50 KB".
Two ways to count bytes
Computers work in binary, so powers of two (1,024 = 2^10) came naturally to early programmers, and "kilo" got borrowed for 1,024 because it was close to 1,000. Later, standards bodies gave the binary units their own names (kibi, mebi, gibi, tebi) and kept kilo, mega and giga for powers of ten, as in every other science.
| Decimal (SI) | Bytes | Binary (IEC) | Bytes |
|---|---|---|---|
| 1 KB (kilobyte) | 1,000 | 1 KiB (kibibyte) | 1,024 |
| 1 MB (megabyte) | 1,000,000 | 1 MiB (mebibyte) | 1,048,576 |
| 1 GB (gigabyte) | 1,000,000,000 | 1 GiB (gibibyte) | 1,073,741,824 |
| 1 TB (terabyte) | 1,000,000,000,000 | 1 TiB (tebibyte) | 1,099,511,627,776 |
The gap grows at each step: about 2.4% at kilo, 4.9% at mega, 7.4% at giga and 10% at tera. That's why nobody notices the difference on a small file, but everyone notices it on a new hard drive.
Why a 1 TB drive shows 931 GB
The box says 1 TB, meaning 1,000,000,000,000 bytes. Windows divides by 1,024 three times and labels the answer "GB":
1,000,000,000,000 ÷ 1,073,741,824 = 931.3
So Windows reports 931 "GB", which is really 931 GiB. The same maths explains other sizes:
| Advertised | Shown by Windows |
|---|---|
| 64 GB | about 59.6 GB |
| 256 GB | about 238.4 GB |
| 500 GB | about 465.7 GB |
| 1 TB | about 931.3 GB |
Macs have shown sizes in decimal units since Mac OS X 10.6, so a Mac shows the same drive as about 1 TB. Phones and other apps vary. Some space is also taken by the operating system, recovery partitions and formatting, so "free space" is always a bit lower again.
Which one does a form mean by "KB"?
This is where it matters in daily life. An exam or job portal says "photo must be under 50 KB". Does it mean 50,000 bytes or 51,200 bytes (50 × 1,024)? The form usually doesn't say, and different websites check differently.
- 50 KB (decimal) = 50,000 bytes
- 50 KiB (binary) = 51,200 bytes
A file of 50,500 bytes passes one check and fails the other. The safe move is to aim for the stricter number: get the file under 50,000 bytes and it passes either way.
There's a second trap. Your computer, phone or app may show sizes in 1,024s while calling them "KB". EveryApp's own tools do this too: the size shown after compressing is in units of 1,024 bytes, labelled KB. A file shown as "49 KB" can be just over 50,000 bytes. For a 50 KB limit, aim for 48 KB or less as shown, and for a 100 KB limit, aim for about 97 KB or less. The guides on compressing an image to 50 KB and PDF size in KB walk through getting there.
To see the exact byte count of a file, check its properties: on Windows, right-click the file and choose Properties; on a Mac, select it and choose Get Info. Both show the size in bytes in brackets.
Converting between them
Open the free unit converter, choose Data size, and pick the units in From and To. Some examples worth knowing:
- Type 1 and convert Terabytes (TB) to Gibibytes (GiB): 931.32... GiB, the number Windows shows.
- Type 50 and convert Kibibytes (KiB) to Bytes: 51,200 bytes.
- Type 2 and convert Mebibytes (MiB) to Megabytes (MB): about 2.097 MB.
The converter also has Bits, which matter for internet speeds. Network speeds are quoted in bits per second, and there are 8 bits in a byte, so a 100 Mbps connection moves at most 12.5 MB of data per second, before any overhead.
If you want to see why 1,024 is a "round" number for a computer, the free number base converter shows it: 1,024 in binary is 10000000000, a 1 followed by ten zeros. The guide to converting binary to decimal explains how that works.
Which should you use?
- Buying storage or reading a spec sheet: decimal (GB, TB). That's how drives, memory cards and phones are sold.
- Reading sizes on Windows: binary, labelled with decimal names. Mentally swap GB for GiB.
- Meeting an upload limit: assume the stricter decimal figure and leave a margin of a few percent.
- Writing technical documents: use KiB, MiB and GiB when you mean 1,024s. It removes all doubt.
Check a size now
Next time a number looks wrong, convert it. The free unit converter has KB, MB, GB, TB and their KiB, MiB, GiB and TiB partners side by side, works on your device, and shows the answer as you type.
Frequently asked questions
- Is 1 KB 1,000 or 1,024 bytes?
- Officially, 1 KB is 1,000 bytes and 1 KiB is 1,024 bytes. In practice, many programs, including Windows, still say KB when they mean 1,024 bytes.
- Why does my 1 TB hard drive only show 931 GB?
- The drive holds 1,000,000,000,000 bytes. Windows divides by 1,024 three times and calls the result GB, which gives 931. It's the same space, counted differently.
- How many bytes is a 50 KB upload limit?
- It depends on the website: 50,000 bytes if it counts in thousands, 51,200 if it counts in 1,024s. Keep your file under 50,000 bytes to be safe.
- What is the difference between MB and MiB?
- An MB is 1,000,000 bytes and an MiB is 1,048,576 bytes, about 4.9% more.
- Is a megabit the same as a megabyte?
- No. A byte is 8 bits, so a megabyte is 8 megabits. Internet speeds use megabits per second (Mbps); file sizes use megabytes.
Calculators
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