Getting started
Enter the actual file size and the speed for the direction you will use. Choosing a file fills its size in B without reading its contents. A realistic upload or download speed is more useful than an advertised maximum. Changing a unit reinterprets the same number, so calculate again afterward.
1 GB at 100 Mbps ideally takes 80 seconds. If you set efficiency to 80%, the estimate becomes 100 seconds. A GiB is larger than a GB. Also,100 MB/s is eight times 100 Mbps. These examples explain the calculation; they are not measurements of your connection.
Rules and limits
Seconds = file bytes × 8 ÷ (bits per second × efficiency/100). One byte is 8 bits;1 GB is 1,000,000,000 B and 1 GiB is 1,073,741,824 B. Efficiency 100% assumes no overhead loss. Positive fractions of a second round up to the next whole second for display; a zero-byte file shows zero.
Efficiency is your assumption, not a measured network average. Connection setup, queues, retransmissions, shared traffic, Wi-Fi and storage speed can change real time. This is not a speed test or a guaranteed completion time. Blank inputs, zero speed, invalid efficiencies and excessively large calculations are rejected. Editing an input hides the previous result.