Why is the real transfer slower than the calculated minimum?

Wi-Fi quality, network congestion, protocol overhead, browser limits, disk speed, and the slower endpoint all add time. The calculator includes a practical overhead estimate.

Is Mbps the same as MB per second?

No. Internet speeds are normally measured in megabits per second, while file sizes use megabytes or gigabytes. Eight bits make one byte.

Should I use upload or download speed?

Use upload speed when you are sending a file and download speed when you are receiving it. Upload speed is often much lower on consumer connections.

Free transfer tool

File transfer time calculator

See how long a large upload or download should take—and why the real result is rarely the theoretical minimum.

Your transfer

Use the upload speed from a recent speed test for the most useful estimate.

File size

Choose the total size of every file in the transfer.

Connection speed

Use upload speed for sending and download speed for receiving.

Include real-world overheadAdds 12% for encryption, protocol overhead, and ordinary connection variation.

Estimated transfer time

7m 28s

A 5 GB file over a 100 Mbps connection, including typical overhead.

Theoretical minimum

6m 40s

Data rate

12.5 MB/s

Keep the tab open?

FileFast uploads large files in recoverable parts, so a brief connection interruption does not have to restart the entire transfer.

Send a large file

Bits are not bytes

A 100 Mbps connection moves at most 12.5 megabytes each second. Internet plans advertise bits; files are measured in bytes.

Upload can be the bottleneck

Many connections download much faster than they upload. Measure the direction you actually need before promising a delivery time.

Leave some margin

Wi-Fi, congestion, encryption, browser work, and the receiving service all add variation. Treat the estimate as a planning range.

Useful context

What changes the result?

Why is my real transfer slower?

Speed tests are a short snapshot. Wi-Fi signal, congestion, protocol overhead, disk speed, and the slower endpoint can all increase the actual time.

What if the connection drops?

A resumable multipart upload can retry only the interrupted part. That is especially important for large files on mobile or unstable Wi-Fi.

Is this also a download calculator?

Yes. Enter the recipient’s download speed instead of your upload speed. The same bit-to-byte calculation applies.