THE CALCULATION WORKSPACE / KEEP THE UNITS
File Size & Transfer Time Calculator
Estimate time from a file total and a rate, keeping decimal, binary and bit units separate.
BEFORE YOU START
An estimate with explicit assumptions.
Choose the total size unit and rate unit carefully: a lowercase b in Mbps means bits, while B in MB/s means bytes. Use nominal mode for an advertised interface rate and effective mode for a known usable rate. A measured rate you enter is your input, not a result measured by this site.
Examples: 10 GB at 100 MB/s is 100 seconds. 10 GiB at 100 MiB/s is 102.4 seconds. 10 GB at a nominal 1 Gbps has an 80-second theoretical lower bound; an optional user-assumed 80% efficiency changes the estimate to 100 seconds.
Units and formula
MB = 1,000,000 bytes; GB = 1,000,000,000 bytes. MiB = 1,048,576 bytes; GiB = 1,073,741,824 bytes. Mbps × 1,000,000 ÷ 8 gives bytes per second; Gbps × 1,000,000,000 ÷ 8 does the same. MB/s and MiB/s multiply by their corresponding byte units.
Time in seconds = bytes ÷ usable bytes per second. In nominal mode an optional efficiency e, greater than 0 and at most 1, changes the denominator to nominal rate × e. In effective mode no efficiency is applied a second time. Zero total size returns zero time; the rate must remain positive.
Interpret the result
A nominal rate is not a device benchmark. Protocol overhead, many small files, software, caching, drive state and other transfers can affect the result. Efficiency is a user assumption, not a value we infer from a device name. Use the copyable calculation to keep the exact units and assumptions with your estimate.