What is Byte/KB/MB/GB Converter (Decimal vs Binary)?
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Bytes to Kilobytes Converter
Bytes, kilobytes, megabytes, gigabytes, terabytes. Decimal (KB = 1000) vs binary (KiB = 1024).
About this converter
A byte is exactly 8 bits (IETF RFC 1700; IEC 80000-13). Larger digital-storage units come in two flavours: SI decimal prefixes (kB, MB, GB, TB based on powers of 10) and IEC binary prefixes (KiB, MiB, GiB, TiB based on powers of 2). Mixing them is the source of the famous "1 TB drive shows 931 GB" mismatch.
How it works
Two parallel prefix systems exist for byte counts. SI prefixes scale by 1,000; IEC binary prefixes scale by 1,024 (= 210):
SI decimal (drive vendors, networking):
1 kB = 10^3 bytes = 1,000 B
1 MB = 10^6 bytes = 1,000,000 B
1 GB = 10^9 bytes = 1,000,000,000 B
1 TB = 10^12 bytes
1 PB = 10^15 bytes
IEC binary (OS RAM, file managers):
1 KiB = 2^10 bytes = 1,024 B
1 MiB = 2^20 bytes = 1,048,576 B
1 GiB = 2^30 bytes = 1,073,741,824 B
1 TiB = 2^40 bytes = 1,099,511,627,776 B
Ratio per step: GiB / GB = 1.0737 (+7.37 percent)
TiB / TB = 1.0995 (+9.95 percent)
Always check which system a number is using. Windows and macOS Finder report binary sizes but label them with decimal prefixes; Linux and most Unix tools default to binary and label correctly with KiB/MiB/GiB.
Worked example
A user buys a "2 TB" external SSD and Windows reports its capacity as 1.81 TB. Is the drive defective?
- Decimal capacity from the manufacturer: 2 TB = 2 x 10^12 bytes = 2,000,000,000,000 bytes.
- Windows internally uses binary: 1 TiB = 2^40 = 1,099,511,627,776 bytes.
- Drive capacity in TiB: 2,000,000,000,000 / 1,099,511,627,776 = 1.819 TiB.
- Windows shows "1.81 TB" (the label is wrong: it should say "1.81 TiB", since the underlying number is binary).
- Subtract ~5 percent for filesystem overhead (NTFS journal, MFT, formatting): user-usable space ~1.72 TiB.
Reference table
| Unit | Decimal bytes | Binary bytes | Real-world equivalent |
|---|---|---|---|
| 1 byte | 1 | 1 | One ASCII letter |
| 1 kB / KiB | 1,000 | 1,024 | ~1 page of plain text |
| 1 MB / MiB | 10^6 | 1,048,576 | 3-min low-res MP3 (low bitrate) |
| 1 GB / GiB | 10^9 | 1,073,741,824 | ~30 minutes of 1080p video |
| 1 TB / TiB | 10^12 | 1,099,511,627,776 | 250,000 MP3 songs |
| 1 PB / PiB | 10^15 | 1,125,899,906,842,624 | One day of Internet Archive crawl |
| 1 EB / EiB | 10^18 | 2^60 | ~1 year of YouTube uploads |
| 1 ZB | 10^21 | 2^70 | Global IP traffic / 2 years (Cisco) |
Common pitfalls
- SI (1 MB = 106) vs IEC (1 MiB = 220). Drive manufacturers use SI: 1 GB = 1,000,000,000 bytes. Windows shows binary but labels them "MB" / "GB": 1 GB displayed = 230 = 1,073,741,824 bytes (which is really a GiB). The gap is 7.37 percent at GB, 9.95 percent at TB.
- Bits vs bytes. Network speeds are bits per second (Mbps), storage is bytes (MB). 1 byte = 8 bits. A 100 Mbps line moves files at 12.5 MB/s. Confusing the two creates an 8x error.
- RAM is binary, storage is decimal. Memory addressing is intrinsically binary, so RAM modules are sold as 8 GB, 16 GB, 32 GB and really mean 8, 16, 32 GiB. SSDs and HDDs are sold in decimal SI. Servers with both never quite line up on capacity arithmetic.
- Formatted vs raw capacity. A "1 TB" drive starts at 1012 bytes (raw), then loses 5 to 7 percent to the filesystem (NTFS MFT, ext4 journal, APFS metadata). Usable space is typically 0.93 to 0.95 TB / 0.85 to 0.88 TiB.
- kbps lowercase b is bits, KBps uppercase B is bytes. Case matters. "kbps" = kilobits per second, "KBps" = kilobytes per second. Most software uses one or the other inconsistently. When in doubt, check whether the number passes the "is it 8x larger than my plan?" smell test.
Related tools and references
Frequently asked questions
What is the difference between KB, MB, GB (SI) and KiB, MiB, GiB (IEC)?
SI decimal prefixes (kilo, mega, giga, tera) use powers of 10: 1 KB = 1,000 bytes, 1 MB = 10^6 bytes, 1 GB = 10^9 bytes. IEC binary prefixes (kibi, mebi, gibi, tebi) use powers of 2: 1 KiB = 1,024 bytes, 1 MiB = 2^20 = 1,048,576 bytes, 1 GiB = 2^30 = 1,073,741,824 bytes. The IEC 80000-13 standard defines the binary prefixes.
Why does my 1 TB hard drive show only 931 GB in Windows?
Drive manufacturers measure capacity in decimal SI (1 TB = 10^12 bytes = 1,000,000,000,000 bytes). Windows reports the same byte count as binary GiB (1 GiB = 2^30 bytes) but labels it "GB". 10^12 / 2^30 = 931.32 GiB. Nothing is missing; the units differ by 7.4 percent and the label is misleading.
How many bits are in a byte, and how are they related to file size?
A byte is exactly 8 bits (IEC 80000-13, RFC 1700). 1 bit holds one binary 0 or 1; 1 byte can encode any value 0-255 or one ASCII character. File sizes are reported in bytes; networking bandwidth is reported in bits per second; divide bandwidth by 8 to estimate file throughput.
Which unit do RAM, SSD, and cloud-storage vendors use?
RAM is sold and addressed in binary (8 GB = 8 GiB = 8,589,934,592 bytes) because memory addressing is intrinsically binary. SSDs and hard drives are sold in decimal SI (1 TB = 10^12 bytes). Cloud-storage providers (AWS S3, Google Cloud, Azure) bill in decimal SI bytes.
Sources
- IEC 80000-13:2008 Quantities and units - Part 13: Information science and technology, defining KiB, MiB, GiB.
- IETF RFC 1700 (1994) Assigned Numbers, byte = 8 bits.
- NIST Special Publication 811 (2008) Guide for the Use of the International System of Units.
- BIPM (2019) The International System of Units (SI), 9th edition, SI prefixes.