Data size converter (bytes, KB, MB, GB)
Storage makers count in powers of 1,000, so 1 GB is 1,000,000,000 bytes, while Windows counts in powers of 1,024, where 1 GiB is 1,073,741,824 bytes; that is why Windows shows a 1 TB drive as about 931 GB. Enter a size in any unit to see it in all of them.
In binary units (KiB, MiB, GiB…)
931.32 GiB
1 TB = 1,000,000,000,000 bytes
- Bytes
- 1,000,000,000,000 bytes1 byte = 8 bits
- Kilobytes (kB)
- 1,000,000,000 kB1 kB = 1,000 bytes
- Megabytes (MB)
- 1,000,000 MB1 MB = 1,000,000 bytes
- Gigabytes (GB)
- 1,000 GB1 GB = 1,000,000,000 bytes
- Terabytes (TB)
- 1 TB1 TB = 1,000,000,000,000 bytes
- Petabytes (PB)
- 0.001 PB1 PB = 1,000,000,000,000,000 bytes
- Kibibytes (KiB)
- 976,562,500 KiB1 KiB = 1,024 bytes
- Mebibytes (MiB)
- 953,674.32 MiB1 MiB = 1,048,576 bytes
- Gibibytes (GiB)
- 931.32 GiB1 GiB = 1,073,741,824 bytes
- Tebibytes (TiB)
- 0.9095 TiB1 TiB = 1,099,511,627,776 bytes
- Pebibytes (PiB)
- 0.0008882 PiB1 PiB = 1,125,899,906,842,624 bytes
- Bits
- 8,000,000,000,000 bits
- Kilobits (kbit)
- 8,000,000,000 kbit1 kbit = 1,000 bits
- Megabits (Mbit)
- 8,000,000 Mbit1 Mbit = 1,000,000 bits
- Gigabits (Gbit)
- 8,000 Gbit1 Gbit = 1,000,000,000 bits
- Terabits (Tbit)
- 8 Tbit1 Tbit = 1,000,000,000,000 bits
- Windows counts in binary units but labels them KB, MB, GB and TB, so it shows 1 TB as roughly 931.32 GB, sometimes with fewer decimals. The drive isn't missing anything; formatting does use a little space on top.
How do you convert between bytes, MB, GB and GiB?
A byte is 8 bits. The SI prefixes are powers of 10: kilo is 1,000, mega 1,000,000, giga 10⁹, tera 10¹² and peta 10¹⁵, so 1 GB is exactly 1,000,000,000 bytes. The international vocabulary of metrology (JCGM VIM) says SI prefixes refer strictly to powers of 10 and should not be used for powers of 2.
Computers address memory in powers of 2, and 2¹⁰ = 1,024 is close to 1,000, so “kilobyte” long meant 1,024 bytes in computing. To end the confusion, the IEC approved binary prefixes in December 1998, now part of IEC 80000-13: kibi (Ki) is 2¹⁰, mebi (Mi) 2²⁰, gibi (Gi) 2³⁰ = 1,073,741,824 and tebi (Ti) 2⁴⁰. Each step is 2.4% bigger than the decimal step, and the gap compounds: a GiB is 7.37% larger than a GB, a TiB 9.95% larger than a TB.
That gap is the “missing” space on a new drive. Drive makers sell in decimal units, and Seagate notes that Windows reports in binary units while still writing GB and TB, so a 1 TB drive (10¹² bytes) shows as 10¹² ÷ 2³⁰ = 931.32 GiB, which Windows labels 931 GB. Apple says iOS 10 and earlier and OS X Leopard and earlier also reported storage in binary units. Formatting takes a little more space on top.
Connection speeds are written in bits per second with decimal prefixes, so divide by 8 to get bytes: 100 Mbit/s (100 Mbps) is 12.5 MB, or 11.92 MiB, a second, and a 1 GB file takes at least 80 seconds on it.
1 byte = 8 bits 1 kB = 1,000 bytes 1 KiB = 1,024 bytes 1 GB = 10⁹ bytes 1 GiB = 2³⁰ = 1,073,741,824 bytes 1 TB in GiB = 10¹² ÷ 2³⁰ = 931.32 MB/s = Mbit/s ÷ 8
How much bigger is each binary unit than its decimal unit?
| Prefixes | Decimal unit | Binary unit | Binary is bigger by | 1 decimal unit in binary |
|---|---|---|---|---|
| kilo (k) · kibi (Ki) | 1 kB = 10³ = 1,000 bytes | 1 KiB = 2¹⁰ = 1,024 bytes | 2.4% | 1 kB = 0.9766 KiB |
| mega (M) · mebi (Mi) | 1 MB = 10⁶ = 1,000,000 bytes | 1 MiB = 2²⁰ = 1,048,576 bytes | 4.86% | 1 MB = 976.56 KiB |
| giga (G) · gibi (Gi) | 1 GB = 10⁹ = 1,000,000,000 bytes | 1 GiB = 2³⁰ = 1,073,741,824 bytes | 7.37% | 1 GB = 953.67 MiB |
| tera (T) · tebi (Ti) | 1 TB = 10¹² = 1,000,000,000,000 bytes | 1 TiB = 2⁴⁰ = 1,099,511,627,776 bytes | 9.95% | 1 TB = 931.32 GiB |
| peta (P) · pebi (Pi) | 1 PB = 10¹⁵ = 1,000,000,000,000,000 bytes | 1 PiB = 2⁵⁰ = 1,125,899,906,842,624 bytes | 12.59% | 1 PB = 909.49 TiB |
| exa (E) · exbi (Ei) | 1 EB = 10¹⁸ = 1,000,000,000,000,000,000 bytes | 1 EiB = 2⁶⁰ = 1,152,921,504,606,846,976 bytes | 15.29% | 1 EB = 888.18 PiB |
| zetta (Z) · zebi (Zi) | 1 ZB = 10²¹ = 1,000,000,000,000,000,000,000 bytes | 1 ZiB = 2⁷⁰ = 1,180,591,620,717,411,303,424 bytes | 18.06% | 1 ZB = 867.36 EiB |
| yotta (Y) · yobi (Yi) | 1 YB = 10²⁴ = 1,000,000,000,000,000,000,000,000 bytes | 1 YiB = 2⁸⁰ = 1,208,925,819,614,629,174,706,176 bytes | 20.89% | 1 YB = 847.03 ZiB |
How to convert a data size between units
- 1Enter the sizeType the number from the box, the file details or the speed test, such as 1, 256 or 100.
- 2Pick its unitChoose the unit it is written in: decimal (kB, MB, GB, TB), binary (KiB, MiB, GiB, TiB), or bits for a connection speed.
- 3Read it in every unitThe result gives the exact number of bytes and the size in every decimal, binary and bit unit, with the most useful one at the top.
- 4Check speeds in bitsFor a speed in megabits, the result also gives bytes per second and how long 1 GB or 1 GiB takes to transfer.
Frequently asked questions
Why does my 1 TB drive show only 931 GB in Windows?
What is the difference between MB and MiB?
How many MB per second is 100 Mbps?
Is a kilobyte 1,000 or 1,024 bytes?
How many bytes are in a gigabyte?
Sources
- BIPM, SI prefixes (kilo 10³ to quetta 10³⁰) (checked 20 Oct 2026)
- JCGM VIM 3, 1.17 multiple of a unit (SI prefixes strictly powers of 10; binary prefixes, source IEC 80000-13) (checked 20 Oct 2026)
- NIST, Prefixes for binary multiples (kibi to exbi, IEC approval in December 1998, 1 B = 8 bit) (checked 20 Oct 2026)
- Seagate, Why does my hard drive report less capacity than indicated on the drive's label? (Windows uses binary; 1 TB shows as 931 GB) (checked 20 Oct 2026)
- Apple Support, How storage capacity is measured on Apple devices (checked 20 Oct 2026)
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