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Transfer time calculator

Estimate file download or upload time from size, rate, and payload efficiency.

◉ Stays in your browser

01 / Your file and connection

File sizeFile size unitTransfer rateRate unitPayload efficiency (%)100% gives the ideal time. For example, 90% reserves 10% of the rate for overhead and other losses.

Assumes a constant transfer rate. Payload efficiency is the share available for file data after overhead, from 0.01% to 100%. This estimate does not measure your connection or model startup delay, congestion, or changing speeds. File size is limited to 1 PB and transfer rate to 1,000 Tbps.

Processed in your browser. No files are uploaded and no connection speed test is run.

Reference: NIST: bits, bytes, and prefixes ↗

02 / Your result

Your result will appear here.
Start with your own input or try an example.

What it does

Estimate how long a file transfer would take at a stated rate. Choose a file-size unit, enter a transfer speed in bits or bytes per second, and set the share of that rate available to file data. Compare the ideal transfer time with the efficiency-adjusted estimate, see the effective payload rate, and export the assumptions alongside your result.

Useful when

Estimate a backup upload using a known sustained connection rate.
Compare expected download durations at two transfer speeds.
Show how a payload-efficiency assumption changes a file-transfer estimate.

How to use it

Enter the file size and select its decimal or binary byte unit.
Enter a positive transfer rate and set payload efficiency from 0.01% to 100%.
Calculate the estimated and ideal times, then copy or download the summary.

A few useful details

What does payload efficiency mean here?

It is the percentage of the entered transfer rate available for file contents. At 90%, a 100 Mbps connection carries 90 Mbps of payload. If you enter an already measured payload rate, use 100% to avoid deducting overhead twice.

How is transfer time calculated?

Convert file size to bytes and transfer rate to bits per second. Estimated seconds = file bytes × 8 ÷ (rate × efficiency ÷ 100). The ideal time uses 100% efficiency. A zero-byte file gives zero seconds.

Will the estimate match a real download exactly?

It assumes a constant rate and a chosen efficiency. Startup delay, congestion, rate changes, disk speed, and competing traffic can change actual time. This tool does not measure the network. Files are limited to 1 PB and rates to 1,000 Tbps.