Download Time Calculator
Estimate how long a file takes to download at a given connection speed. Enter a file size and a bandwidth and get the time — worked out instantly in your browser.
How download time is calculated
Estimating a download is simple arithmetic once every value is in the same units. The formula is time = total bits ÷ bits per second. A file's size in bytes is multiplied by 8 to get bits, and the connection speed is converted to bits per second, then one is divided by the other. For a 1 GB file over a 100 Mbps line that is 8,000,000,000 bits ÷ 100,000,000 bits/s = 80 seconds.
The trap that catches almost everyone is the difference between bits and bytes. Internet providers advertise speed in bits per second — Mbps, megabits — while files are measured in bytes. Because a byte is 8 bits, a 100 Mbps connection tops out at roughly 12.5 megabytes per second, not 100. This calculator keeps the two straight for you: pick a bit-based unit like Mbps for your line speed, or a byte-based unit like MB/s if you are reading a transfer meter.
Real downloads never quite hit the theoretical time. Protocol overhead, latency, disk speed, server limits, and congestion all take a slice, so treat the result as a best case. A good rule of thumb is to add 10–20% for TCP and application overhead on top of the raw number.
There is also a units question. Providers and drive makers use decimal units where 1 GB is exactly 1,000,000,000 bytes, so this tool defaults to base 1000. Your operating system may report the same file as smaller because it counts in binary units (1 GiB = 1,073,741,824 bytes). Flip the binary-units toggle to match whichever number you started with. To dig into why speed and delay are different things, see our guide on bandwidth vs latency, and for the bigger picture read how data travels the internet.
Everything is computed locally — nothing you type leaves your browser. Planning the packet-level side of a transfer? The MTU & MSS Calculator shows how much payload fits per packet, and the Number Base Converter helps with the bits-and-bytes maths.
Frequently asked questions
How long does 1 GB take to download at 100 Mbps?
About 80 seconds, in ideal conditions. A 1 GB file is 8 billion bits (1,000,000,000 bytes × 8), and 100 Mbps is 100 million bits per second, so 8,000,000,000 ÷ 100,000,000 = 80 seconds. Real downloads are slower because of protocol overhead, latency, and shared bandwidth.
Why is a 100 Mbps connection not 100 MB per second?
Network speeds are quoted in bits per second, while file sizes are in bytes, and there are 8 bits in a byte. So 100 Mbps is only about 12.5 MB per second at best. Mixing up bits and bytes is the single most common reason download-time estimates come out eight times wrong.
Should I use 1000 or 1024 for units?
Network and storage marketing use decimal units where 1 GB is 1,000,000,000 bytes, so this calculator defaults to base 1000. Operating systems often report sizes in binary units where 1 GiB is 1,073,741,824 bytes. Toggle "binary units" if your file size came from a file manager that uses 1024-based sizes.
Is this download calculator private?
Yes. The calculation runs entirely in your browser with JavaScript. Nothing you enter is uploaded, logged, or shared — it is just arithmetic on the numbers you type.
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