Download time calculator
Estimate a download’s duration from file size and speed (fibre, 4G, ADSL).
- Instant
- Free
- Private (processed locally)
- No sign-up
How long for this download?
Before starting a big file, you would like to know. This tool computes the duration from size and speed, handles the byte/bit conversion, and compares common connections at a glance.
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Enter the size
In MB, GB or TB.
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Enter the speed
In Mbps or Gbps (the advertised speed).
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Read the duration
And compare fibre, 4G and ADSL in the chart.
Example: a 1 GB file
| Connection | Duration |
|---|---|
| Fibre 1 Gbps | 8 s |
| Fibre 100 Mbps | 1 min 20 s |
| 4G (50 Mbps) | 2 min 40 s |
| ADSL (8 Mbps) | 16 min 40 s |
Basis: 1 byte = 8 bits, decimal speeds (1 Gbps = 1,000,000,000 bits/s). It is a theoretical minimum; real time is longer.
Frequently asked questions
Why doesn’t 1 GB download in 1 second at 1 Gbps?
Because one byte is 8 bits. A 1 GB file = 8 billion bits; at 1 Gbps (1 billion bits per second), it therefore takes 8 seconds in theory. This is the most common confusion between GB (size) and Gbps (speed).
Why is the real time longer?
The advertised speed is a theoretical maximum. In practice, latency, the protocol (TCP), the source server, Wi-Fi and congestion reduce usable throughput. Allow a margin: the calculation gives the irreducible minimum, rarely reached.
How do I read Mbps and MB units?
The lowercase “b” means bit (speed, e.g. 100 Mbps), the uppercase “B” means byte (size, e.g. 700 MB). Providers bill in bits per second; files are measured in bytes. The tool converts automatically.
Which typical speeds should I use?
As a guide: fibre 1 Gbps or 100 Mbps, 4G around 50 Mbps, ADSL around 8 Mbps. The chart applies these speeds to your file to compare durations at a glance.