Download time calculator
Enter file size and speed, get the download time.
How long will my download take?
Time = file size in bits ÷ speed in bits per second. A 1 GB file at 100 Mbps: 8,000 megabits ÷ 100 = 80 seconds, at full speed.
Why do I multiply by 8?
File sizes are in bytes (B), internet speeds in bits per second (b). One byte is 8 bits, so 100 Mbps moves 12.5 megabytes per second.
What is the difference between GB and GiB?
NIST: a gigabyte (GB) is 10⁹ bytes; a gibibyte (GiB) is 2³⁰ = 1,073,741,824 bytes. Operating systems often show sizes in binary units while labeling them GB.
Why is my real download slower?
The calculator assumes the full advertised speed the whole time. Network overhead, Wi-Fi, other users and the server’s own speed all slow things down.
What speed do I need for video?
The FCC’s broadband guide suggests about 5–8 Mbps for HD video streaming.
Worked example: a 25 GB game on a 300 Mbps connection
Convert the size to bits: 25 GB = 25 × 10⁹ bytes × 8 = 200 × 10⁹ bits. Divide by the speed in bits per second: (200 × 10⁹) ÷ (300 × 10⁶) = 667 seconds, which is 11 min 7 s. The same connection moves 300 ÷ 8 = 37.5 megabytes per second. If the file is actually 25 GiB, the size is 25 × 2³⁰ = 26,843,545,600 bytes and the time is 11 min 56 s. A smaller case: a 500 MB update on a 25 Mbps connection takes 2 min 40 s.
How do I allow for a slower real-world speed?
The time is inversely proportional to the speed you actually get, so divide the calculator's time by the share of the advertised speed you expect. If the 25 GB game gets 75% of 300 Mbps, the time grows from 11 min 7 s to 14 min 49 s; at 50% it is 22 min 13 s. Measure your real speed with a speed test during a download rather than relying on the figure on the plan.
What speed do I need to finish in a set time?
Turn the formula around: speed = file size in bits ÷ time in seconds. To download 25 GB in 10 minutes you need (25 × 10⁹ × 8) ÷ 600 = 333 megabits per second, sustained for the whole time. Round up for overhead, since the calculation assumes nothing else uses the connection.
How much do GB and GiB differ?
NIST explains that the binary prefixes kibi, mebi and gibi (Ki, Mi, Gi) were created because computer makers used “kilo” and “mega” for powers of 1,024 while telecommunications and drive makers use powers of 1,000. The gap grows with each step: a gibibyte is 7.4% larger than a gigabyte, and a tebibyte is 10.0% larger than a terabyte. Telecommunications engineers use a megabit per second for 10⁶ bits per second, so the speed figure follows the decimal convention. Choose the unit the file size was given in, and expect your operating system to show a different number for the same file.
Common mistakes with download times
Mixing bits and bytes: a speed of 300 Mbps is megabits, and a browser may show megabytes per second, so the same link appears as 37.5. Reading 300 Mbps as 300 megabytes per second would shrink the 25 GB example to 1 min 23 s. Using the upload speed of a plan for a download, or the reverse; they are listed separately. Expecting the advertised speed for the whole transfer: the figure is a maximum and the calculator’s result is a best case. And comparing sizes in different prefixes: check whether a game launcher or operating system shows GB or GiB.
Sources and related calculators
Sources: NIST, “Prefixes for binary multiples” (kibi, mebi, gibi, tebi and the origin of the confusion); Federal Communications Commission, Broadband Speed Guide (HD streaming range quoted above). Related: data storage converter, speed converter, time calculator and reading time calculator.