Download time calculator
Enter the file size and your connection speed to see how long the transfer takes. The tool keeps bits and bytes apart (a 100 Mbps line moves 12.5 MB per second) and decimal MB apart from binary MiB. Add an overhead percentage to model a connection that never reaches its full advertised speed.
Runs in your browser: nothing you enter is sent anywhere.
How to use it
- Enter the file size and choose its unit. Use MB or GB for sizes quoted by a website, and MiB or GiB for sizes shown by some operating systems.
- Enter your speed and its unit. Internet plans use Mbps, download managers often show MB/s.
- Optionally enter an overhead. Try 5 to 10 percent for a typical connection.
- Read the time. The effective speed row shows the speed after overhead in both units.
Time (s) = size in bytes × 8 ÷ (speed in bit/s × (1 − overhead ÷ 100)).
Worked example
A 1 GB file (10⁹ bytes = 8 × 10⁹ bits) on a 100 Mbps connection takes 8 × 10⁹ ÷ 10⁸ = 80 seconds, or 1 min 20 s. With 10 percent overhead the effective speed is 90 Mbps and the time becomes 80 ÷ 0.9 = 88.9 seconds.
Tips
- If a speed test says 94 Mbps on a 100 Mbps plan, enter 94 and leave overhead at 0.
- Large files may also be limited by the server, disk speed or Wi-Fi, which no calculator can see.
Frequently asked questions
Why is my download slower than the speed my provider advertises?
Advertised speeds are bits per second on the line, and a download shows bytes per second, which is one eighth of that. On top of this, headers, retransmits, Wi-Fi quality and server limits take a share, so real downloads often reach 85 to 95 percent of the line speed. Use the overhead box to include this.
What is the difference between Mbps and MB/s?
Mbps is megabits per second and MB/s is megabytes per second. One byte is 8 bits, so 100 Mbps is 12.5 MB/s. Providers quote Mbps, while download managers and browsers usually show MB/s.
What is the difference between MB and MiB?
MB is a decimal megabyte of 1,000,000 bytes, and MiB is a binary mebibyte of 1,048,576 bytes. Storage makers use MB and GB, while some operating systems use binary units but call them MB and GB. A 1 GiB file is about 7.4 percent larger than 1 GB.
How is the time calculated?
Time in seconds = file size in bytes × 8 ÷ (speed in bits per second × (1 − overhead ÷ 100)). Overhead of 0 percent means the full speed is used.
Does this work for uploads?
Yes. The arithmetic is the same, so enter your upload speed instead of your download speed.