File size plus connection speed equals download time — with MB vs MiB handled properly and a realistic-speed estimate.
Internet speeds are usually quoted in bits (Mbps), while file sizes are in bytes: 1 byte = 8 bits. MB uses powers of 1,000; MiB uses powers of 1,024.
Overheads and congestion mean real downloads rarely hit the headline speed; 85% is a reasonable planning figure.
download time (at full speed)
How to use this tool
With its unit — MB, GB, TB, or the binary MiB/GiB if your software reports those.
Usually in Mbps from your plan or a speed test; MB/s is also accepted.
Full-speed time and a realistic time at your chosen efficiency.
The time for 1 GB at this speed helps judge any file size at a glance.
Formula & worked example
1 GB (1,000,000,000 bytes) at 100 Mbps: 8,000,000,000 / 100,000,000 = 80 seconds. At 85% real-world efficiency that becomes about 94 seconds. 1 GiB takes slightly longer, 85.9 seconds at full speed.
Limitations — read this before you rely on it
Headline speeds are maximums, not guarantees; Wi-Fi, server limits, other devices and protocol overhead all slow real downloads. File sizes quoted by operating systems often use GiB while download managers use GB, a ~7% difference at the gigabyte scale.
Frequently asked questions
Speeds are quoted in bits, files in bytes (divide by 8), and overhead, Wi-Fi and server limits cut the real rate further.
MB = 1,000,000 bytes (decimal); MiB = 1,048,576 bytes (binary). Operating systems often display MiB but label it MB.
800 seconds (13 min 20 s) at full speed, or about 15 min 40 s at 85% efficiency.
No: Mbps is megabits per second. Divide by 8 for megabytes per second — 100 Mbps is 12.5 MB/s.
Roughly 25 Mbps sustained for one 4K stream, plus headroom for other devices.