Last updated: October 2026
How long does a download take?
Short answer: a 100 GB file on a 100 Mbps connection takes about 2 hours 23 minutes (2.39 hours) in theory. In practice, add 5–10% for network overhead — so budget around 2 hours 30 minutes. Enter your file size and speed in the calculator above for an exact estimate.
How the download time formula works
The math is simple: time = (file size in bytes × 8) ÷ speed in bits per second. File sizes are measured in bytes, but connection speeds are advertised in bits — and one byte holds 8 bits. So a 100 Mbps connection moves at most 12.5 megabytes per second. Learn more in Wikipedia's bit rate article.
Common examples: a 5 GB movie on a 50 Mbps connection takes about 13–14 minutes; a 50 GB game on a 200 Mbps fiber line takes about 35 minutes; a 2 TB backup on gigabit (1 Gbps) needs roughly 4½ hours.
Units used here
To match how the real world works, this calculator uses 1024-based units for file sizes (1 GB = 1024 MB, the way operating systems count) and decimal units for speeds (1 Mbps = 1,000,000 bits per second, the way internet providers advertise). That is also why estimates vary slightly between tools — there is no single agreed standard for a "gigabyte".
Frequently asked questions
Why is my download slower than the estimate?
The calculator shows the theoretical minimum: file size divided by your connection speed. Real downloads are slower because of network overhead (protocol headers add about 5–10%), congestion on your line or the server, and Wi-Fi signal loss. If your actual time is far worse than the estimate, run a speed test to see what speed you're really getting.
What is the difference between Mbps and MB/s?
Mbps means megabits per second; MB/s means megabytes per second. There are 8 bits in a byte, so divide megabits by 8 to get megabytes. A 100 Mbps connection can download at most 12.5 MB/s. Internet providers advertise speeds in bits (Mbps), while browsers usually show downloads in bytes (MB/s) — that 8x difference is the biggest source of confusion.
Does the calculator account for network overhead?
No — it shows the pure transfer time. TCP/IP headers, encryption and retransmission add roughly 5–10% on top of the theoretical time. Treat the result as the best possible case: if it says 2 hours, expect somewhere between 2 hours and 2 hours 12 minutes in the real world.
Can I use this for upload time too?
Yes — the math is identical. Enter your upload speed (check it with a speed test, since upload speeds are usually much lower than download speeds) instead of your download speed, and the estimate works the same way.
Is my data private?
Completely. Every calculation runs locally in your browser with JavaScript — nothing you enter is sent to a server, stored, or tracked.
