Why does a 100 Mbps line not download a 100 MB file in one second?

Speed is in megabits while files are in megabytes, and there are eight bits per byte. A 100 MB file is 800 megabits, so even at 100 Mbps it needs roughly eight seconds before overhead.

Does the calculator use 1024 or 1000 for file size units?

File sizes use binary multiples, so 1 MB is 1024 KB and 1 GB is 1024 MB. The connection speed, however, uses 1 Mbps = 1,000,000 bits per second, matching how ISPs advertise speeds.

Is the estimated time the real-world download time?

It is the theoretical best case at the full advertised speed. Actual transfers are usually slower because of protocol overhead, network congestion, server limits, and shared bandwidth.

Can I use it for uploads too?

Yes. Enter your upload speed in Mbps instead of download speed, and the same calculation gives the estimated time to send the file.

Bandwidth Calculator

File Size

Size Unit

Bandwidth100 Mbps

Transfer Time1m 26s

File Size (bytes)1,073,741,824

This bandwidth calculator estimates how long it takes to transfer a file over a connection of a given speed. You enter the file size and the link speed in megabits per second, and it returns the transfer time in a readable hours-minutes-seconds form. It bridges the common mismatch between file sizes, which are quoted in bytes, and connection speeds, which are quoted in bits per second.

Formula

time (s) = (fileSizeBytes × 8) / (Mbps × 1,000,000)

fileSizeBytes: File size in bytes (KB×1024, MB×1024², GB×1024³, TB×1024⁴)
Mbps: Connection speed in megabits per second
× 8: Converts bytes to bits, since speeds are quoted in bits

How it works

Enter the file size as a number and choose its unit (KB, MB, GB, or TB), where each step is 1024 times the one below it.
Enter the connection speed in megabits per second (Mbps); the tool treats one Mbps as 1,000,000 bits per second.
The file size is converted to bits (bytes times eight) and divided by the speed in bits per second to give the transfer time, which is shown as ms for sub-second results or as a combined h/m/s string otherwise.

Worked example

How long to download a 2 GB file over a 100 Mbps connection?

Convert size to bytes: 2 × 1024³ = 2,147,483,648 bytes.
Convert to bits: 2,147,483,648 × 8 = 17,179,869,184 bits.
Divide by speed: 17,179,869,184 ÷ (100 × 1,000,000) ≈ 171.8 seconds.

About 171.8 seconds, displayed as 2m 52s.

Frequently asked questions

Why does a 100 Mbps line not download a 100 MB file in one second?: Speed is in megabits while files are in megabytes, and there are eight bits per byte. A 100 MB file is 800 megabits, so even at 100 Mbps it needs roughly eight seconds before overhead.
Does the calculator use 1024 or 1000 for file size units?: File sizes use binary multiples, so 1 MB is 1024 KB and 1 GB is 1024 MB. The connection speed, however, uses 1 Mbps = 1,000,000 bits per second, matching how ISPs advertise speeds.
Is the estimated time the real-world download time?: It is the theoretical best case at the full advertised speed. Actual transfers are usually slower because of protocol overhead, network congestion, server limits, and shared bandwidth.
Can I use it for uploads too?: Yes. Enter your upload speed in Mbps instead of download speed, and the same calculation gives the estimated time to send the file.

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