Estimate how long a file will take to download from its size, connection speed and real-world efficiency.
The estimate assumes a steady connection. Server limits, other users, Wi-Fi quality and network congestion can change actual time.
How to use the Download Time Calculator
Enter the file size and select KB, MB, GB or TB. Then enter the connection speed shown by your broadband plan or speed test in Kbps, Mbps or Gbps. Add an efficiency percentage to produce a more realistic estimate.
Download time formula
| Step | Calculation |
|---|---|
| Convert file to bits | File bytes × 8 |
| Effective speed | Connection bits per second × efficiency percentage |
| Download time | File bits ÷ effective bits per second |
Bits and bytes are different
Broadband speed is normally advertised in bits per second, while files are normally measured in bytes. One byte contains eight bits. This is why a 100 MB file does not take one second on a 100 Mbps connection under ideal conditions; it needs roughly eight seconds before overhead.
Why actual downloads can be slower
Advertised speed is not guaranteed for every transfer. Wi-Fi signal, busy networks, distance from equipment, server limits, device performance and other household activity can reduce throughput. A wired speed test can help provide a better input.
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Ofcom’s broadband speed guidance explains factors that can reduce real-world connection performance and recommends testing at different times.
Frequently asked questions
Why do bytes need to be multiplied by eight?
Network speeds are measured in bits, and each byte of file data contains eight bits.
What efficiency percentage should I use?
Use a recent measured speed where possible. Otherwise, a cautious figure such as 80% to 90% can illustrate overhead and variation.
Does the calculator use MB or MiB?
It uses decimal MB, where one MB is 1,000,000 bytes.
Why is my real download slower than the estimate?
Wi-Fi, congestion, server limits, other users and device performance can reduce the effective speed.
Can I calculate a large game download?
Yes. Enter its stated size in GB or TB and use your measured download speed for the best estimate.