Need bytes, kilobytes, and tebibytes in one place? Type a size above, pick a unit, and copy SI (1000), IEC (1024), and bit values. This file size converter is part of the programming tools on TechOpt.io, next to the UUID generator.
How this file size converter splits SI vs IEC
Two unit systems sit on top of the same byte. SI (the International System of Units) steps by 1,000: 1 kB = 1,000 bytes, 1 MB = 1,000 kB, 1 GB = 1,000 MB, 1 TB = 1,000 GB. IEC binary prefixes step by 1,024: 1 KiB = 1,024 bytes, 1 MiB = 1,024 KiB, 1 GiB = 1,024 MiB, 1 TiB = 1,024 GiB. See multiple-byte units for the naming.
Drive makers, cloud invoices, and network specs usually use SI. Operating systems, RAM, and file systems usually use IEC — even when the UI still says “GB”. This converter never mixes them: MB is always 106 bytes and MiB is always 220 bytes.
KB vs KiB
People still write KB for both 1,000 and 1,024 bytes. The unambiguous names are kB / KB for 1,000 bytes and KiB for 1,024 bytes. The same split applies at every magnitude:
| SI (decimal) | Bytes | IEC (binary) | Bytes |
|---|---|---|---|
| 1 kB | 1,000 | 1 KiB | 1,024 |
| 1 MB | 1,000,000 | 1 MiB | 1,048,576 |
| 1 GB | 1,000,000,000 | 1 GiB | 1,073,741,824 |
| 1 TB | 1,000,000,000,000 | 1 TiB | 1,099,511,627,776 |
In code, prefer the IEC names or an explicit power of two (1 << 20 for a mebibyte) when the size is a memory page, a buffer, or a block size. Prefer SI when you are matching a vendor’s advertised capacity or a decimal quota.
Why 1 TB is not 1 TiB
A “1 TB” drive is 1,000,000,000,000 bytes. Divide by 230 (a gibibyte) and you get about 931.32 GiB. Divide by 240 and you get about 0.91 TiB. Windows File Explorer still labels that binary result as GB, which is why a new disk looks smaller than the box.
The same gap shows up on every advertised disk: 8 TB is about 7.28 TiB. If you are planning an array rather than converting a single size, use the RAID calculator for mdadm usable capacity.
Bits vs bytes
A byte is 8 bits. File sizes, object storage, and RAM are in bytes (MB, GiB). Link speeds and throughput are in bits per second (Mbit/s, Gbit/s). A 1 Gbit/s link can move 125 MB of payload per second before protocol overhead. Mixing Mbit and MB by a factor of eight is a common source of “the upload is too slow” confusion.
FAQ
Why does a 1 TB drive show as 931 GiB?
Drive makers advertise decimal terabytes: 1 TB = 10^12 bytes. Operating systems usually report tebibytes (1 TiB = 2^40 bytes), and File Explorer often labels GiB as GB. 1,000,000,000,000 ÷ 2^30 ≈ 931.32 GiB. Toggle TB and GiB above to see both.
What is the difference between KB and KiB?
KB (or kB) is 1,000 bytes (SI). KiB is 1,024 bytes (IEC). The same split applies at every step: MB vs MiB, GB vs GiB, TB vs TiB. Use KiB/MiB/GiB when you mean binary; use kB/MB/GB when you mean decimal.
Is 1 MB 1000 KB or 1024 KB?
In SI, 1 MB = 1,000 kB = 1,000,000 bytes. Older computer usage said “MB” for 1,048,576 bytes, which is a mebibyte (MiB) now. This converter treats MB as 10^6 bytes and MiB as 2^20 bytes so the two never get mixed.
How many bytes are in a gigabyte?
1 GB (SI) is 1,000,000,000 bytes. 1 GiB is 1,073,741,824 bytes. RAM and file systems usually mean GiB even when the UI says GB.
What is the difference between bits and bytes?
A byte is 8 bits. File sizes are in bytes (MB, GiB). Link speeds are in bits per second (Mbit/s, Gbit/s). A 1 Gbit/s link moves 125 MB per second of payload, ignoring protocol overhead.
Does Windows use GB or GiB?
File Explorer divides by 1,024 but labels the result GB, MB, or KB. A 1,073,741,824-byte file shows as 1.00 GB. This converter calls that 1 GiB and 1.07 GB so you can see both.
Does this file size converter upload my values?
No. It runs entirely in your browser. The number you type never leaves your machine.
Looking for more developer how-tos? Browse the programming guides or the rest of the tools.