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Bandwidth Calculator

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Calculate file transfer time from size and connection speed — with a realistic estimate (adjustable efficiency, default 80%) shown alongside the theoretical one, not just a theoretical number presented as if it were real.

How it works

  1. Enter a file size and connection speed — theoretical transfer time appears instantly
  2. Adjust the efficiency slider (default 80%, the commonly cited real-world range) to see a realistic estimate alongside it
  3. The Mbps-vs-MB/s (bits vs bytes) relationship is always spelled out explicitly below the result

Frequently asked questions

Why is there a difference between theoretical and realistic time?

The theoretical figure assumes 100% use of the rated connection speed. In practice, protocol overhead, Wi-Fi loss, and network congestion mean real-world throughput is commonly around 70–80% of the advertised speed — this tool defaults to 80% but you can adjust it.

What's the difference between Mbps and MB/s?

Mbps is megabits per second (how connection speeds are usually advertised); MB/s is megabytes per second (how file sizes are usually measured). 1 byte = 8 bits, so Mbps ÷ 8 = MB/s.

Where does the 80% default come from?

It's the middle of the commonly cited 70–80% range for real-world throughput versus advertised speed — not a precise measurement of your specific connection, which is why it's adjustable.

Is any of my data sent to a server?

No — the calculation runs entirely in your browser.

#BandwidthCalculator#DownloadTimeCalculatorRealistic#MbpsToMb/sConverter#FileTransferTimeCalculator#InternetSpeedTheoreticalVsActual

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From the blog

A download time calculator that admits its own number isn't realistic — then gives you only that number anyway
dev

A download time calculator that admits its own number isn't realistic — then gives you only that number anyway

One existing tool labels its comparison chart "not necessarily realistic values," then hands you a single theoretical download time with no realistic alternative in sight.

2026-08-30

Update history

  • 2026-08-30 Added: a cover image (two speedometer gauges — one at max, one lower with a dashed gap arc — over a pipe of data flowing to a file icon, with a small ratio icon hinting at the bit/byte relationship) — used as the card thumbnail, social share image, and blog title image.
  • 2026-08-30 Launched: live bandwidth/download-time calculator (no button) — theoretical transfer time alongside an adjustable realistic estimate (default 80% efficiency), with the Mbps/MB/s (bits vs bytes) relationship always spelled out. Entirely client-side.