Bandwidth Calculator
Two tools in one: convert between data-rate units (bits and bytes, decimal and binary multiples), and estimate how long a file transfer takes at a given sustained speed. Results update as you type, entirely in your browser.
Data-rate converter
Example: 100 Mbit/s is 12.5 MB/s.
Transfer-time estimator
Example: 1 GB at 100 Mbit/s takes 1 min 20 s.
Bits vs. bytes — the source of almost every confusion
Networks measure in bits per second; files are measured in bytes, and a byte is eight bits.
That single factor explains the classic disappointment: a "100 megabit" connection moves at
most 12.5 megabytes per second, so a 1 GB download takes about
1 min 20 s even under perfect conditions — a figure this page computes with the same engine
as the calculator above. Watch the capitalization: lowercase
b is bits, uppercase B is bytes.
Decimal vs. binary multiples
Network and storage vendors use decimal multiples (1 MB = 1,000,000 bytes), while operating systems often use binary ones (1 MiB = 1,048,576 bytes). Both unit families are available in the converters so you can match whichever convention your source uses instead of guessing — and the ~7% gap between GB and GiB stops looking like missing data.
Reading the estimate honestly
The transfer estimate is the mathematical floor: size ÷ sustained rate. Real-world transfers add protocol overhead, TCP slow start, shared-medium contention on Wi-Fi, and server-side limits. A practical rule of thumb is to expect 5–10% over the ideal time on a wired connection and more on wireless — if reality is far worse, measure the actual link speed first with the converter to rule out a bits/bytes misreading.
Frequently asked questions
Why does my 100 Mbps connection download at only about 12 MB/s?
Because network speeds are quoted in megaBITS per second and file sizes in megaBYTES — and one byte is eight bits. 100 Mbit/s ÷ 8 = 12.5 MB/s is the theoretical ceiling; protocol overhead takes a few percent more.
What is the difference between MB and MiB?
MB (megabyte) is decimal: 1,000,000 bytes. MiB (mebibyte) is binary: 1,048,576 bytes. Drive manufacturers and networks use decimal units; operating systems often report binary ones, which is why a "500 GB" drive shows as ~465 GiB.
Why do real transfers take longer than the estimate?
The calculator gives the ideal time at a perfectly sustained rate. Real transfers add TCP/IP and protocol overhead (typically 2–10%), speed variation, server limits, and Wi-Fi contention. Treat the result as a best-case floor.
Are Gbit/s and Gbps the same thing?
Yes — “bps” is just an abbreviation of bit/s. Watch the capitalization elsewhere, though: a lowercase b means bits and an uppercase B means bytes, so 1 GBps is eight times faster than 1 Gbps.
Values are processed locally in your browser and never transmitted. Conversions are implemented as tested, typed functions — see the methodology page.