A file may be labelled in megabytes while a connection is advertised in megabits per second. The similar names hide an exact factor of eight: one byte contains eight bits. Capitalization matters too. MB/s is a byte rate, while Mbit/s or Mbps is a bit rate. DownloadTime asks for the unit beside each entered number so that the conversion remains visible rather than being guessed from context. This distinction is the first check whenever an expected transfer time seems eight times too short or too long.

Convert the rate before dividing

The duration formula needs compatible quantities. A decimal 100 MB file contains 100,000,000 bytes, or exactly 800,000,000 bits. At 100 Mbit/s, the rate is 100,000,000 bits each second, so the ideal duration is eight seconds. The same numeric rate written as 100 MB/s is eight times larger: 800,000,000 bit/s, giving one second. Do not remove the factor of eight because both labels contain the letter M. Normalize size and rate to bits, retain the exact fraction, and only then format the duration for reading.

Keep GB and GiB separate

Decimal prefixes use powers of 1000: 1 GB is exactly 1,000,000,000 bytes. Binary prefixes use powers of 1024: 1 GiB is exactly 1,073,741,824 bytes. Therefore 100 GB and 100 GiB are not interchangeable inputs. At a decimal 100 Mbit/s, 100 GB takes exactly 8,000 seconds at ideal line rate, while 100 GiB takes 8,589.934592 seconds. DownloadTime offers both unit families explicitly. Choose the symbol reported by the file source instead of silently treating familiar wording as a binary quantity.

Copy the unit, not only the number

When gathering inputs, note the complete label from the file listing, transfer application, provider page, or another source you trust. A displayed 12.5 MB/s is equivalent to 100 Mbit/s, but a displayed 12.5 Mbit/s is not. If the source uses an ambiguous word such as “megabytes” without a symbol or definition, the ambiguity cannot be solved by arithmetic. Check that source before calculating. DownloadTime never inspects the file or connection on your behalf; it calculates only from the size, rate, and units you deliberately enter.