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About this tool
Calculate how long a file or dataset takes to transfer at a given link speed, with protocol overhead and unit conversions handled.
This calculator computes file transfer time as size in bits divided by effective link rate — the formula time = (bytes × 8) ÷ (bit rate × efficiency) — converting correctly between bits and bytes and between decimal (GB, powers of 1000) and binary (GiB, powers of 1024) units. It is for anyone planning a backup window, cloud migration, video upload or dataset sync who wants to know whether the move takes minutes, hours or days at their line speed.
Open Bandwidth Transfer Time Calculator on AltFTool — it loads instantly in your browser.
Enter the values you already know.
Fine-tune the options to match your scenario.
Read the result and use it in your planning or reporting.
Link speeds are bits per second, file sizes are bytes — the 8× conversion is built in, not forgotten.
GB (1000³) and GiB (1024³) are separate options, so Windows-reported sizes convert correctly.
Shows ideal time and the extra minutes added by protocol overhead side by side.
About 80 seconds in theory: 1 GB is 8,000,000,000 bits, and 100 Mbps moves 100,000,000 bits per second. With a realistic 90% protocol efficiency it comes to roughly 89 seconds — around a minute and a half.
Because plans are sold in megaBITS per second and file managers report megaBYTES per second, which are 8 times larger units. A 100 Mbps plan therefore tops out at 12.5 MB/s before any protocol overhead — that factor of 8 is the single most common source of confusion.
A gigabyte (GB) is 1,000,000,000 bytes under the SI convention used by drive makers and macOS, while a gibibyte (GiB) is 1,073,741,824 bytes (1024³) as used by Windows and most programming contexts. The difference is about 7.4%, which matters on multi-terabyte transfers.
The formula gives a best case for a sustained, uncontended link. Real transfers lose throughput to TCP/IP header overhead and acknowledgements (typically 5-10%), latency limiting the TCP window on long routes, slow disks at either end, and competing traffic — which is why the calculator lets you set an efficiency percentage.
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