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Download Time Calculator (File Size and Internet Speed)

Work out how long a file of a given size takes to download or upload at a given connection speed, in megabits or megabytes per second, with an allowance for real-world throughput and comparisons at common speeds.

Last updated: October 2026

Download time

66.67 minutes

Formula below · 3 sources (physics.nist.gov, fcc.gov, bipm.org) · Updated Oct 2026

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About this calculator

Transfer time is simply data divided by rate, once both are in the same units. Files are measured in bytes and connections in bits per second, and a byte is 8 bits, so a file of S megabytes at a speed of R megabits per second takes 8S ÷ R seconds. A 50 GB game at 100 Mbps is 400,000 megabits ÷ 100 Mbps = 4,000 seconds, about 67 minutes. Forgetting the factor of 8 is the most common mistake and makes every estimate eight times too optimistic.

The calculator converts the size to bits with the exact factor for its unit (decimal GB = 10⁹ bytes, binary GiB = 2³⁰ bytes) and the speed to bits per second (Mbps = 10⁶ bits per second; MB/s = 8 × 10⁶ bits per second), then divides. The efficiency field scales the speed down to what you really get: protocol headers, acknowledgements and Wi-Fi retransmissions typically leave 85-95% of the rated line speed for payload on a wired connection and often less on Wi-Fi, and the remote server may be the bottleneck altogether. Leave it at 100% for the theoretical minimum, or set it to a measured speed-test share for a realistic estimate.

The same arithmetic applies to uploads, which are usually much slower than downloads on cable and DSL plans, and to copying over a local network, where a gigabit link moves about 110 MB/s in practice.

How to use

Example (the defaults): a 50 GB download on a 100 Mbps connection at 100% efficiency. 50 GB = 50 × 10⁹ bytes = 4 × 10¹¹ bits = 400,000 Mb. 400,000 Mb ÷ 100 Mbps = 4,000 s = 66.67 minutes (1.11 hours). The tiles show the same file at 25 Mbps (266.7 min) and 1 Gbps (6.67 min). A 4.7 GB film on 25 Mbps at 90% efficiency: 4.7 × 8 × 10⁹ = 37,600 Mb; effective speed 22.5 Mbps; 37,600 ÷ 22.5 = 1,671 s = 27.85 minutes. A 250 MB upload at 10 Mbps: 2,000 Mb ÷ 10 Mbps = 200 s = 3.33 minutes. Enter the speed in MB/s if your download manager reports it that way: 12.5 MB/s is the same as 100 Mbps.

Frequently asked questions

Why does a 100 Mbps connection not download 100 MB per second?

Because the speed is in megabits and the file in megabytes. 100 Mbps is 100 ÷ 8 = 12.5 MB per second at best, and after protocol overhead typically 11-12 MB/s. Internet plans are advertised in bits per second precisely because the numbers are eight times larger. Always check whether a figure says Mb (bits) or MB (bytes).

How long does a 1 GB download take?

At 100% efficiency: 1 GB = 8,000 Mb, so 8,000 ÷ speed in Mbps seconds. That is 13.3 minutes at 10 Mbps, 5.3 minutes at 25 Mbps, 80 seconds at 100 Mbps, 16 seconds at 500 Mbps and 8 seconds at 1 Gbps. Multiply by about 1.1 for a realistic figure on a wired connection, more on Wi-Fi or a busy server.

What efficiency should I enter?

If you have run a speed test, divide the measured download speed by your plan speed: 94 Mbps measured on a 100 Mbps plan is 94%. Without a measurement, 90% is reasonable for a wired connection and 60-80% for Wi-Fi away from the router. Even then a slow remote server, a VPN, or other devices streaming at the same time can dominate; the calculator cannot see those, so treat the result as a floor rather than a promise.

Does it matter whether the file size is in GB or GiB?

By 7.4% at the gigabyte scale. Windows reports sizes in binary units but labels them GB, so a file shown as 50 GB there is 50 GiB = 53.7 GB, which takes 7.4% longer to download than a true 50 GB. If the size comes from Windows Explorer choose GiB; if it comes from a download page, a Mac or a Linux tool it is normally decimal GB.

Why is my upload so much slower than my download?

Cable and DSL plans are asymmetric: a 300/20 plan gives 300 Mbps down but only 20 Mbps up, so uploading the same file takes fifteen times longer. Fibre plans are often symmetric. Enter your upload speed in the speed field to estimate an upload, a cloud backup or a video call recording transfer.

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