Free download time calculator. Enter a file size in GB or GiB and a speed in Mbps to see how long the download takes, and what the other unit would give.
The three DVD capacities are quoted from ECMA-267, which states them in decimal Gbytes. The last two rows are the definitions themselves: a drive sold as 1 TB, and the memory that NIST notes is counted in binary.
| Item | As labelled | On the other convention |
|---|---|---|
| DVD-5, one layer | 4.7 GB | 4.38 GiB |
| DVD-9, two layers | 8.5 GB | 7.92 GiB |
| DVD-10, two sides | 9.4 GB | 8.75 GiB |
| Drive labelled 1 TB | 1 TB | 0.91 TiB |
| Memory module, 8 GiB | 8 GiB | 8.59 GB |
Protocol overhead alone is computable, and it is smaller than most estimates: at the usual 1500-byte MTU, an IPv4 packet spends 20 bytes on its IP header and 20 on the TCP header, leaving 1460 bytes of payload. That is 97.3% of the IP packet, or 94.9% of everything Ethernet puts on the wire once framing, preamble and the interframe gap are counted. Everything below that comes from congestion, server limits, Wi-Fi and distance, which no formula can predict for you, so the efficiency field is yours to set from a speed test rather than a number we invent.
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Enter the file size and your connection speed and this calculator gives the transfer time, the throughput in MB/s, and the clock time it finishes. It also tells you which byte convention it used, because two calculators can disagree by 7 percent on the same file and neither of them usually says why.
A transfer moves bits, so the time is the file expressed in bits divided by the connection rate in bits per second. The subtlety is the word megabyte. Internet rates are always decimal: 100 Mbps is 100,000,000 bits per second, never 104,857,600. File sizes are not. A storage vendor means 1,000,000 bytes by a megabyte and a file manager usually means 1,048,576, and the gap compounds to 7.4 percent at gigabyte scale. This calculator offers both ladders under the binary-prefix names NIST publishes, so GB is always 10⁹ bytes and GiB is always 2³⁰, and the answer says which one produced it.
Download Time Formula
Store pages quote game sizes in decimal GB, so leave the unit on GB for a launcher figure.
A device reports its own capacity in GiB even when the box said GB, which is why a 128 GiB restore takes longer than a 128 GB one.
A DVD image is 4.7 GB decimal and a CD image is 700 MiB binary, which is the clearest example of the two conventions living side by side.
On satellite or rural DSL the efficiency field matters more than the headline rate, because congestion takes a larger share of a smaller pipe.
A 100 GB game at 100 Mbps takes about two and a quarter hours. At 10 Mbps it takes most of a day, which is a different decision.
The comparison table puts your file against five connection tiers at once, which is a more honest answer than a single number about whether an upgrade is worth paying for.
If another calculator gave you a different time for the same file, it is almost always the byte convention. This page shows both readings side by side.
Set the efficiency field from a speed test instead of assuming you get the number on the bill.
Almost always the byte convention. One reads GB as 1,000,000,000 bytes and the other as 1,073,741,824, a difference of 7.4 percent. Both are in common use: NIST notes that storage manufacturers mean the decimal value while memory manufacturers mean the binary one. Neither is a mistake, but a calculator that does not say which it used leaves you unable to reconcile the two answers. This page names the convention and shows the other reading beside the result.
Under the SI prefixes, 1 GB is exactly 1,000,000,000 bytes and 1,073,741,824 bytes is 1 GiB, a gibibyte. In practice a download page or a drive label usually means the decimal figure, while Windows and most file managers display the binary one while still writing GB. If your number came from a file manager, choose GiB here.
Mbps is megabits per second and is what an ISP sells you. MB/s is megabytes per second and is what a download manager shows. There are 8 bits in a byte, so 100 Mbps is 12.5 MB/s at most. Both are decimal: the megabit and megabyte prefixes in a transfer rate are powers of ten, which is why the rate side of this calculation is never ambiguous.
Protocol overhead is the small, predictable part. At a 1500-byte MTU an IPv4 and TCP header pair costs 40 bytes, leaving 1460 bytes of payload, so around 97.3 percent of the IP packet carries your file, or about 94.9 percent once Ethernet framing is counted. The rest is congestion, server-side limits, Wi-Fi interference and distance to the server, none of which a formula can predict. Run a speed test and put the result in the efficiency field.
At 100 Mbps a 100 GB decimal file takes about 2 hours 13 minutes at the full advertised rate. At 25 Mbps it is about 8 hours 53 minutes, and at 1 Gbps about 13 minutes. If the launcher reports the size as 100 GiB instead, add roughly 7 percent to each figure.