Bandwidth & Download Time Calculator
Estimate how long it takes to transfer a file at a given connection speed. Handles bits vs bytes and decimal (MB) vs binary (MiB) units correctly.
Estimated transfer time
1m 20s
- Seconds
- 80
- Minutes
- 1.33
- Hours
- 0.02
- Days
- 0
Time = file size (in bits) ÷ bandwidth (in bits per second). 1 byte = 8 bits exactly (IEC 80000-13). Network speed prefixes are decimal (Mbps = 10⁶ bits/s) per IEEE 802; binary prefixes (MiB = 2²⁰ B) are kept distinct from decimal (MB = 10⁶ B). Real-world transfers are ~10–20% slower due to TCP overhead, retransmits and disk write speed.
How to use this calculator
Enter the file size and pick the unit it is reported in — disk and download labels are usually decimal (MB, GB), while Windows file properties and RAM use binary (MiB, GiB). Enter your connection speed and choose its unit — internet plans are quoted in megabits per second (Mbps), while file managers report transfer rates in megabytes per second (MB/s). The headline shows the predicted time; the breakdown converts it into seconds, minutes, hours and days.
How the calculation works
The calculator converts the file size to bits (1 byte = 8 bits, IEC 80000-13) and the connection speed to bits per second, then divides. Decimal SI prefixes (1 MB = 10⁶ B) follow the IEEE / hard-drive convention; binary IEC prefixes (1 MiB = 2²⁰ B) follow the convention used by operating systems for RAM and file size. The two differ by ~4.9% at the megabyte level and ~7.4% at gigabytes — enough to matter for a 100 GB transfer. The result is a theoretical minimum; real downloads run ~10–20% slower because TCP/IP overhead, retransmits, server throttling and disk write speed all eat into raw line rate.
Worked example
Downloading a 1 GB (decimal) file on a 100 Mbps connection: 1 GB = 8 × 10⁹ bits; 100 Mbps = 10⁸ bits/s; time = 80 seconds (1 min 20 s) in the ideal case. On a 100 MiB binary file at the same speed: 100 × 2²⁰ × 8 ÷ 10⁸ = 8.39 s. A 4.7 GB DVD image over a 10 MB/s USB drive: 4.7 × 10⁹ ÷ 10⁷ = 470 s = 7 min 50 s.
Frequently asked questions
Why is my actual download slower than this estimate?
This is the theoretical minimum at full line rate. In practice you lose ~10–20% to TCP overhead (acknowledgements, window scaling), packet retransmits on lossy links, server-side throttling, and on big files the bottleneck shifts to your disk write speed. A 1 Gbps fibre link rarely sustains more than ~110 MB/s end-to-end; a Wi-Fi 5 link rarely beats ~50 MB/s. Multiply the headline number by 1.2–1.3 for a realistic upper-bound.
What is the difference between Mbps and MB/s?
Megabits versus megabytes — a factor of 8. Internet plans are sold in Mbps (megabits per second) because the number looks bigger. File managers report MB/s (megabytes per second) because files are measured in bytes. A "100 Mbps" plan tops out at 12.5 MB/s; a "1 Gbps" plan at 125 MB/s. Always check the unit before comparing.
Why does GB on a hard drive differ from GiB in Windows?
Hard-drive makers use decimal (SI) gigabytes: 1 GB = 10⁹ bytes. Windows (and many older OSes) use binary gibibytes but label them "GB": 1 GiB = 2³⁰ bytes ≈ 1.0737 × 10⁹ B. So a "1 TB" drive shows as ~931 GB in Windows — the storage is identical, the units differ by 7.4%. Linux and macOS now use the correct decimal labels. IEC 80000-13 (2008) standardised KiB / MiB / GiB to end the ambiguity.
What counts as a good home internet speed in 2026?
For one person streaming and browsing: 50 Mbps is fine. For a household with multiple 4K streams, cloud backup and video calls: 200–500 Mbps is comfortable. Gigabit (1000 Mbps) is the cap on most consumer fibre and is overkill for streaming but useful for moving large files (a 50 GB game downloads in ~7 minutes versus ~70 minutes on 100 Mbps). Upload speed matters separately if you back up to cloud or stream live — many cable plans throttle upload below 50 Mbps even on gigabit down.
Does this work for uploads as well as downloads?
Yes — the maths is symmetric. Use your upload speed (often much lower than download on cable / ADSL) for upload time estimates. Cloud backup services and video uploads to YouTube or Vimeo will be bottlenecked by your upstream link, not your downstream one.
How does this handle very slow or very large transfers?
The result is shown as milliseconds for sub-second transfers, seconds for quick ones, and a "Xh Ym" breakdown for anything past a minute. The breakdown panel always shows the answer in seconds, minutes, hours and days so you can pick the unit that fits — a 1 PB cold-storage migration over a 1 Gbps link comes out to ~93 days, which is more informative than "8.0 × 10⁶ s".