How to use
- Choose How long will it take? or What speed do I need?
- Enter the file size and pick the unit (GB, MB, GiB…).
- Enter your connection speed, or the time you want the transfer to take.
- Optionally add protocol overhead (5–10% is typical) for a realistic estimate.
Options explained
- Mbps vs MB/s
- Providers advertise megabits per second; download apps show megabytes per second. 100 Mbps is at most 12.5 MB/s.
- GB vs GiB
- GB is decimal (1,000 MB), GiB is binary (1,024 MiB). Windows labels GiB as “GB”, so a “10 GB” file in Windows is about 10.7 GB.
- Protocol overhead
- TCP/IP headers, Wi-Fi and retransmissions mean real throughput is usually 5–10% below the line speed.
Formulas and examples
seconds = size in bytes × 8 ÷ (speed in bits per second × (1 − overhead))
speed needed = size in bytes × 8 ÷ seconds ÷ (1 − overhead)A 50 GB game at 300 Mbps takes 50 × 8 × 10^9 ÷ 300 × 10^6 = 1,333 seconds, or 22 minutes 13 seconds. With 10% overhead it is 1,481 seconds, or 24 minutes 41 seconds. To send a 2 GB video in 10 minutes you need 2 × 8 × 10^9 ÷ 600 = 26.7 Mbps.
| Speed | Time for 1 GB |
|---|---|
| 10 Mbps | 13 min 20 s |
| 50 Mbps | 2 min 40 s |
| 100 Mbps | 80 s |
| 300 Mbps | 26.7 s |
| 1,000 Mbps | 8 s |
The same file is bigger in GiB: 1 GiB is 1.0737 GB, so it takes 85.9 s at 100 Mbps.
Frequently asked questions
Why is my download slower than the calculation?
The server, Wi-Fi signal, other devices on your network and the route between you and the server all limit speed. The result is the best case for your line speed.
Does it work for uploads?
Yes. Enter your upload speed — on many home connections it is much lower than the download speed.
What speed is my connection?
Your plan’s advertised speed is the maximum. A speed test shows what you actually get; use that number for a more realistic estimate.
Privacy
This tool runs entirely in your browser. Your files and text are processed on your device and are never uploaded to our servers.