Byte Conversion Calculator
Convert any digital storage size between bits, bytes, kilobytes, megabytes, gigabytes, terabytes, and petabytes. Choose between binary (base-1024, used by operating systems) or decimal (base-1000, used by drive manufacturers) to see exactly why a "1 TB" drive appears smaller on your computer. The optional download-time panel tells you how long a file of that size takes to transfer at any connection speed.
Formula
Worked example
1 GB (binary) = 1,073,741,824 bytes = 8,589,934,592 bits. At 100 Mbps (100,000,000 bps) that downloads in (8,589,934,592 / 100,000,000) = 85.9 seconds.
Binary vs decimal: why your drive looks smaller than advertised
There are two competing unit conventions for digital storage. Operating systems (Windows, macOS, Linux) use binary units where each step is a factor of 1,024: one kilobyte is 1,024 bytes, one megabyte is 1,048,576 bytes, and so on. Hard drive and SSD manufacturers use decimal (SI) units where each step is 1,000: one kilobyte is exactly 1,000 bytes. A drive labeled "1 TB" by its maker holds 1,000,000,000,000 bytes, but your OS divides that by 1,099,511,627,776 (one binary terabyte) and displays the result as roughly 909 GB. Neither value is wrong; they simply use different but well-defined standards. The IEC introduced the labels kibibyte (KiB), mebibyte (MiB), and gibibyte (GiB) in 1998 specifically to disambiguate the two systems, though most operating systems still display the older KB/MB/GB symbols for binary values.
Bits vs bytes and network speeds
One byte equals eight bits. Storage capacity is almost always quoted in bytes (or their multiples), while network and internet speeds are almost always quoted in bits per second, usually megabits per second (Mbps) or gigabits per second (Gbps). To convert a network speed to a download rate in megabytes per second, divide the Mbps figure by 8. A 100 Mbps connection delivers about 12.5 MB/s of actual data, so a 1 GB file takes roughly 80 seconds at that speed (ignoring protocol overhead). This calculator outputs both megabits (Mb) and gigabits (Gb) so you can compare file sizes directly against the bandwidth figures quoted by ISPs.
How the download time estimate works
Enable the download time panel and choose a connection speed preset (or enter a custom speed). The calculator converts the file size to bits, then divides by the connection speed in bits per second. The result is a theoretical minimum; real transfers are typically 5-20% slower because TCP/IP headers, TLS encryption, and server-side throttling add overhead. Mobile connections add further variability. Use the estimate for planning purposes, not for SLA commitments.
Choosing the right mode
Use binary mode when you want to match what your file manager reports. Use decimal mode when comparing against hard drive specifications, cloud storage quotas, or telecommunications standards. Most cloud providers (AWS S3, Google Drive, Dropbox) bill in decimal gigabytes, so a 50 GB plan holds exactly 50,000,000,000 bytes, which your OS may report as about 46.6 GB in binary mode. When precision matters, check the provider documentation for which convention applies.
Binary vs decimal storage units compared
| Unit | Binary value (OS) | Decimal value (drive maker) | Difference |
|---|---|---|---|
| 1 KB | 1,024 bytes | 1,000 bytes | 2.4% |
| 1 MB | 1,048,576 bytes | 1,000,000 bytes | 4.9% |
| 1 GB | 1,073,741,824 bytes | 1,000,000,000 bytes | 7.4% |
| 1 TB | 1,099,511,627,776 B | 1,000,000,000,000 B | 9.9% |
| 1 PB | 1,125,899,906,842,624 B | 10^15 B | 12.6% |
Why a "1 TB" drive shows as ~931 GB in your OS: the units differ by up to 7.4% at the TB level.
Frequently asked questions
Why does my 1 TB hard drive show less than 1 TB on my computer?
Drive manufacturers define 1 TB as 1,000,000,000,000 bytes (decimal). Your operating system measures the same space in binary units, where one terabyte is 1,099,511,627,776 bytes, so it reports the drive as about 909 GB. Toggle this calculator to decimal mode and binary mode side by side to see the exact difference for any drive size.
What is the difference between Mb (megabit) and MB (megabyte)?
Capitalization matters: uppercase B means byte, lowercase b means bit. One byte equals eight bits. Megabits (Mb) are used for network speeds (your ISP advertises in Mbps), while megabytes (MB) are used for file sizes and storage capacity. To convert Mbps to MB/s, divide by 8.
How many bytes are in a petabyte?
In binary mode (OS-reported), one petabyte is 2 to the power of 50 bytes, which equals 1,125,899,906,842,624 bytes. In decimal mode (SI/drive-maker), one petabyte is exactly 1,000,000,000,000,000 bytes. The difference between the two is about 12.6%. Hyperscale data centers commonly use the decimal definition.
How long does it take to download a 1 GB file at 100 Mbps?
1 GB (binary) is 1,073,741,824 bytes, or 8,589,934,592 bits. At 100,000,000 bits per second that is 85.9 seconds in theory. Real-world TCP/IP overhead and server limits typically add 10-20%, so expect around 95-105 seconds. Use the download time panel in this calculator to get estimates for any size and speed combination.
What is the difference between a kilobyte (KB) and a kibibyte (KiB)?
A kilobyte (KB) in the binary convention equals 1,024 bytes, the value used by operating systems. A kibibyte (KiB), defined by IEC 80000-13, also equals 1,024 bytes and was introduced to distinguish binary-1024 prefixes from SI-decimal prefixes, where 1 kB = 1,000 bytes. In practice most OS file managers display KB but mean KiB.