Download Time Calculator — file size and internet speed

How it works

Estimating a download time is just size divided by speed, but there is one catch that trips almost everyone up: files and connections are measured in different units. File sizes use megabytes (MB) — a byte is 8 bits — while internet speeds are quoted in megabits per second (Mbps). Because one byte is 8 bits (NIST), you multiply the file size by 8 before dividing:

time (seconds) = (8 × file MB) ÷ speed Mbps

That factor of 8 is why a "100 Mbps" connection downloads a 100 MB file in about 8 seconds, not 1 — the connection moves 100 megabits each second, but the file is 100 megabytes = 800 megabits.

This is a best-case estimate. Real downloads are slower because of network overhead, server limits, Wi-Fi losses and congestion, so treat the result as a floor.

Worked example

A 1000 MB file over a 100 Mbps connection takes 8 × 1000 ÷ 100 = 80 seconds (1:20). A small 8 MB song over 20 Mbps is almost instant at 3.2 seconds; a 4.7 GB movie (4700 MB) over 100 Mbps takes 8 × 4700 ÷ 100 = 376 seconds (about 6¼ minutes); and a 50 GB game over a fast 500 Mbps line needs 8 × 50000 ÷ 500 = 800 seconds, or about 13 minutes.

Frequently asked questions

How do I calculate download time?

Divide the file size by the connection speed, matching the units. Since files are in megabytes and speeds in megabits, and a byte is 8 bits, use time = (8 × file MB) ÷ speed Mbps to get seconds.

Why multiply by 8?

Because a byte is 8 bits. File sizes are given in megaBYTES (MB) but internet speeds in megaBITS per second (Mbps). Multiplying the megabytes by 8 converts the file into megabits so it matches the speed unit before you divide.

Why is my real download slower than this estimate?

This is the theoretical best case. Actual speeds are reduced by network overhead (protocol headers, acknowledgements), server and Wi-Fi limits, congestion at peak times, and the fact that advertised speeds are maximums. Expect real downloads to take somewhat longer.

What is the difference between MB and Mb?

MB (megabyte, capital B) is a unit of file size; Mb (megabit, lowercase b) is a unit of data rate, and 1 MB = 8 Mb. Internet plans advertise megabits per second (Mbps) because the number looks bigger — a "100 Mbps" plan delivers about 12.5 MB per second.

How long to download a 1 GB file?

A 1 GB file is about 1000 MB. Over a 100 Mbps connection that is 8 × 1000 ÷ 100 = 80 seconds; over a 50 Mbps connection, 160 seconds; over 1000 Mbps (gigabit), about 8 seconds. Enter your own size and speed above for an exact figure.

Does this use 1 MB = 1000 or 1024 bytes?

This calculator uses the SI/decimal convention, 1 MB = 1,000,000 bytes, which is how storage and bandwidth are usually advertised (and how NIST defines the SI prefixes). The binary units — 1 MiB = 1,048,576 bytes — differ by about 5% for megabytes and more for larger sizes.