About the Download Time Calculator
This download time calculator estimates how long a file will take to transfer at a given connection speed — a game update, a 4K movie, a cloud backup or a large dataset. Enter the file size in KB, MB, GB or TB (or the binary MiB/GiB units your operating system may show) and your speed in Mbps, Gbps or MB/s, and it returns the time in hours, minutes and seconds.
It works just as well for uploads: use your upload speed, which on cable and DSL plans is often a tenth of the download speed. The comparison chart shows the same transfer at common plan speeds from 10 Mbps to 2 Gbps, so you can judge whether an upgrade would really make a difference.
Internet speeds are sold in megabits per second while file sizes are in megabytes, and 1 byte = 8 bits — the most common source of confusion. The overhead setting (10% by default) accounts for TCP/IP headers, Wi-Fi losses and server limits; TCP/IP headers alone take about 5% of each full-size Ethernet packet, so even a perfect wired link delivers roughly 95% of its line rate as file data.
With the default inputs, the estimated transfer time is 6m 58s. Change any value above to recalculate instantly.
How to use the download time calculator
- 1Enter the file size and choose its unit (GB, MB, GiB…).
- 2Enter your download or upload speed from a speed test or your plan.
- 3Pick the speed unit — Mbps for most internet plans, MB/s for download managers.
- 4Adjust the overhead (10% is realistic; 0% is the theoretical minimum).
- 5Read the estimated time and compare other plan speeds in the chart.
Formula and method
The file size is converted to bytes (decimal units: 1 GB = 1,000,000,000 bytes; binary units: 1 GiB = 1,073,741,824 bytes) and multiplied by 8 to get bits, because connection speeds are measured in bits per second. The advertised speed is converted to bits per second and reduced by the overhead percentage to get the effective throughput.
Dividing the number of bits by the effective speed gives the transfer time in seconds. The estimate assumes a steady speed for the whole transfer; in practice speeds vary with server load, Wi-Fi signal and other devices sharing the connection.
- size
- File size in bytes
- speed
- Connection speed in bits per second (100 Mbps = 100,000,000)
- overhead
- Share of the bandwidth lost to protocols and conditions
Worked examples
4.7 GB DVD image on 100 Mbps
4.7 GB is 37.6 billion bits. With 10% overhead, 100 Mbps delivers 90 Mbps (11.25 MB/s), so the download takes 37.6e9 ÷ 90e6 ≈ 418 seconds — just under 7 minutes.
50 GB game on 300 Mbps fibre, best case
50 GB × 8 = 400 billion bits. At a full 300 Mbps that is 400e9 ÷ 300e6 = 1,333 seconds, about 22 minutes.
Uploading a 1 TB backup at 20 Mbps
1 TB is 8 trillion bits. At 20 Mbps less 10% overhead (18 Mbps) it takes 8e12 ÷ 18e6 ≈ 444,444 seconds — about 123.5 hours, or over 5 days of continuous uploading.
700 MiB file at 5 MB/s
700 MiB is 734,003,200 bytes. At 5 MB/s (40 Mbps) that is 734,003,200 ÷ 5,000,000 = 146.8 seconds, about 2½ minutes.
Frequently asked questions
How long does 1 GB take to download at 100 Mbps?+
About 80 seconds in theory (8,000 megabits ÷ 100 Mbps) and roughly 90 seconds in practice once around 10% overhead is included.
What is the difference between Mbps and MB/s?+
Mbps is megabits per second, used for internet plans; MB/s is megabytes per second, shown by browsers and download managers. There are 8 bits in a byte, so 100 Mbps is 12.5 MB/s.
Why is my download slower than my plan speed?+
Protocol overhead, Wi-Fi interference, other devices using the connection and the server’s own upload limit all reduce throughput. A wired connection close to the router usually gets closest to the advertised speed.
Why does my computer show a different file size?+
Windows reports sizes in binary units (1 GB shown = 1 GiB = 1,073,741,824 bytes) while storage makers and most websites use decimal units (1 GB = 1,000,000,000 bytes). Choose GiB or MiB to match Windows.
How do I calculate upload time?+
Use the same formula with your upload speed. Many cable and DSL plans upload at only 5–20% of their download speed, so backups and video uploads take much longer than downloads.