Download Time Calculator
Estimate how long a file takes at a given connection speed.
What you provide
How much of the rated speed a real transfer achieves. 85% is typical on a wired connection.
Result
About 7.8 min at 100 Mbps
The arithmetic assumes the connection is the bottleneck, and often it is not. A single download can be limited by the server, by a slow disk at your end, or by the size of the TCP window on a long path, and none of those improve when you buy a faster line. On Wi-Fi, the link to the router usually decides the outcome long before the internet connection does. Treat this as the floor on time rather than the expected time.
- File size5000 MB, or 40000 megabits
- 5 GB
- Connection
- 100 Mbps
- At the full rated speed
- 6.7 min
- At 85% efficiency
- 7.8 min
- Effective throughput
- 10.6 MB/s
- If the speed halvesWorth knowing before starting a large transfer on a shared connection
- 15.7 min
What this cannot tell you
- Arithmetic on the figures you enter. It does not test your connection or download anything.
- It assumes your connection is the bottleneck. A slow server, a busy disk or a single stream on a high-latency path can all make a transfer slower than this, and none of them improve with a faster line.
Take this with you
How this calculation works
The file size is converted to bits, the connection speed to bits per second, and one divided by the other gives the theoretical time. An efficiency setting then adjusts for the share of a link that never carries payload, which is a few percent on wired Ethernet and considerably more on Wi-Fi. Both figures are shown, because the gap between them is worth seeing rather than hiding behind one number.
What the results mean
- At the full rated speed
- The theoretical floor. No transfer beats it, and almost none reach it.
- At your efficiency setting
- A realistic estimate for a connection that is otherwise idle and a server that can keep up.
- If the speed halves
- What happens when someone else starts streaming. Useful before committing to a large transfer on a shared line.
Common problems and fixes
- The download is far slower than the estimate
- Check whether anything else is using the connection, then check where the file is coming from. A single-source download is limited by the slowest point in the chain, which is frequently the server rather than your line. Downloads that arrive in parallel chunks, as most software updates do, get closer to the estimate because they are not waiting on one stream.
- Speed starts fast and then drops
- Usually a buffer emptying rather than a fault. The first seconds come from a cache close to you, and once that is exhausted the rate settles to what the origin can sustain. On mobile connections a sustained drop can also mean a data allowance threshold has been passed and the connection has been shaped.
Frequently asked questions
Why divide by eight?
Because connection speeds are quoted in bits per second and file sizes in bytes, and a byte is eight bits. A 1 GB file over a 100 Mbit/s connection is 8,000 megabits divided by 100, which is 80 seconds at best and closer to 95 in practice.
Does a faster connection always mean faster downloads?
Only up to the point where something else becomes the bottleneck. Beyond a few hundred megabits, a single download is often limited by the server, by disk write speed, or by the TCP window on a long path. That is why upgrading a fast connection frequently makes less difference than expected.
What efficiency figure should I use?
Around 85% on a wired connection, and 40% to 60% on Wi-Fi, where shared airtime and management traffic take a much larger share. If you have timed a real transfer before, work backwards from it: divide the throughput you actually saw by the rated speed of the link.
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