⏱️ Download Time Calculator
Enter a file size and your connection speed to see how long the transfer takes — both the theoretical best and a realistic estimate.
Estimated real-world download time
1 m 29 s
Theoretical best: 1 m 20 s
Time = file size in bits ÷ speed in bits per second. Watch the units: speeds are quoted in bits (Mbps) but files in bytes (MB), and there are 8 bits per byte — so a 1 GB file on a 100 Mbps line takes about 80 seconds, not 10. Real transfers run ~10–20% slower than the theoretical rate because of protocol overhead and congestion. 🔒 In your browser.
How the download time calculator works
Transfer time is the file size in bits divided by the connection speed in bits per second. The catch that trips everyone up is units: internet speeds are quoted in bits (Mbps) but file sizes in bytes (MB), and there are eight bits in a byte — so a 1 GB file on a 100 Mbps line takes about 80 seconds, not 10. The tool converts both sides to a common base, and can knock ~10% off the ideal rate to account for the protocol overhead and congestion that make real transfers slower.
Your real speed is usually below the advertised figure — Wi-Fi, the server's upload limit, congestion and TCP/IP overhead all cut into it. The "real-world overhead" option applies a 90% efficiency factor as a rough guide; a busy or distant server can be much slower. Uploads use your upload speed, which on many home connections is far lower than the download speed.
Frequently asked questions
How do I calculate download time?
Download time = file size ÷ speed, with both in the same units. Convert the file to bits (bytes × 8) and divide by the speed in bits per second: a 1 GB file over 100 Mbps is 8,000,000,000 bits ÷ 100,000,000 = 80 seconds.
Why does my download take longer than calculated?
Advertised speeds are a maximum you rarely hit. Wi-Fi loss, a slow or busy server, distance, and protocol overhead all reduce real throughput — typically by 10–20% or more. Enable the overhead option for a more realistic figure.
Is 100 Mbps the same as 100 MB/s?
No — and this is the most common mistake. 100 Mbps (megabits) is only 12.5 MB/s (megabytes), because a byte is 8 bits. So a 100 Mbps connection downloads a 1 GB file in about 80 seconds, not 10.
How long to download a 1 GB file?
On 100 Mbps, roughly 80 seconds theoretically (about 90 with overhead); on 1 Gbps, about 8 seconds; on 10 Mbps, about 13 minutes. Enter your exact speed for a precise figure.
Does this work for uploads too?
Yes — just enter your upload speed instead of download. On many home connections upload is much slower than download, so uploading a large file can take far longer than downloading the same file.