About the Download Time Calculator
Whether it is a game update, a film, a backup or a large work file, it helps to know how long a download or upload will take before you start. The sum looks simple — size divided by speed — but two things trip people up. Internet speeds are sold in megabits per second, while files are measured in megabytes, and a byte is eight bits. And real connections never quite reach the advertised speed, because some of the capacity is used by the network itself.
This download time calculator works out the time to transfer a file from its size and your connection speed, with an allowance for overhead. It gives the realistic time, the ideal time at the full speed, the transfer rate in megabytes per second, the speed you would need to finish within a target time, and how much you could transfer in an hour.
How to Use the Download Time Calculator
Enter the file size and choose its unit, from MB to TB, or MiB and GiB if your software shows binary units.
Enter the connection speed and its unit. Broadband and mobile plans are usually given in Mbps or Gbps; some download managers show MB/s.
Set the overhead, the share of the speed lost to protocols, Wi-Fi and real-world conditions. 10 percent is a sensible default; use more for busy Wi-Fi or distant servers.
Optionally, enter a target time in minutes to see what speed would be needed.
How Download Time Is Worked Out
bits = file size in bytes × 8
real speed = advertised speed × (1 − overhead)
time = bits ÷ real speed
speed needed = bits ÷ target seconds ÷ (1 − overhead)
MB per second = real speed in Mbps ÷ 8Step-by-Step Example
A 5 GB file on a 100 Mbps connection, allowing 10 percent overhead.
Bits: 5 GB × 8 = 40 gigabits = 40,000 megabits
Real speed: 100 Mbps × 0.9 = 90 Mbps
Time: 40,000 ÷ 90 = 444 seconds = 7 min 24 s
Ideal: 40,000 ÷ 100 = 400 seconds = 6 min 40 s
Rate: 90 ÷ 8 = about 11.3 MB a secondSo expect about 7 minutes 24 seconds. At this speed you could transfer about 40.5 GB an hour.
To finish the same file in 2 minutes, 120 seconds, you would need 40,000 ÷ 120 = 333 Mbps at full efficiency, or about 370 Mbps allowing 10 percent overhead. A gigabit connection would do it comfortably: a 1 Gbps line moves up to 125 MB a second, and would bring down a 50 GB game in about 7 minutes 24 seconds with the same overhead.
Bits, Bytes and Speed Units
The factor of eight is the most common source of surprise. A 100 Mbps plan can never show more than 12.5 MB a second in a download window, and usually shows a little less. Upload speeds follow the same rule, but on many home connections they are much slower than download speeds, so sending a large file can take far longer than receiving it. With 20 Mbps upload and 10 percent overhead, a 5 GB file takes about 37 minutes.
If your software shows GiB rather than GB, choose GiB as the unit: a 5 GiB file is about 7 percent larger than 5 GB and takes correspondingly longer.
What Slows Downloads Down
Several things keep real speeds below the advertised figure. Every packet of data carries addressing and error-checking information, which uses a few percent of the capacity. Wi-Fi adds more loss, especially through walls or with many devices connected. The server sending the file may be busy or far away and limit how fast it sends. Other people in the home streaming or downloading share the same connection. And broadband plans often quote a speed that is reached at off-peak times rather than guaranteed all day.
A wired connection to the router, downloading at quieter times and pausing other large transfers are the simplest ways to get closer to the full speed.
Big Downloads in Practice
Game and system updates of 50 to 100 GB are now common. On a typical 100 Mbps home connection, at about 40.5 GB an hour, they take one to three hours. On a 20 Mbps connection, with no overhead, a 4 GB film takes about 26 minutes 40 seconds, and a large game could take most of a day. Knowing the time in advance lets you start big downloads overnight or when the connection is otherwise idle.
Understanding Your Result
The headline is the realistic transfer time, allowing for the overhead you set.
The ideal time is what the transfer would take at the full advertised speed.
The rate shows the expected speed in megabytes a second, as most download windows display it.
The speed needed shows the connection required to finish within your target time.
The per hour figure shows how much data you could move in an hour.
When Should You Use This Calculator?
Use it before starting a large download or update, to plan when to begin.
Use it to estimate how long a backup or cloud upload will take on your upload speed.
Use it when choosing a broadband plan, to see what a faster speed would save.
Use it to check whether a download is running as fast as your connection should allow.
Common Mistakes
Mixing up Mbps and MB/s. Divide megabits per second by 8 to get megabytes per second.
Expecting the full advertised speed. Allow for overhead, Wi-Fi and busy servers.
Using download speed for uploads. Upload speeds are often much slower.
Ignoring binary units. A size in GiB is about 7 percent larger than the same number in GB.
Forgetting other users. Everyone on the same connection shares its speed.