Download Time Calculator

Enter the file size, choose MB or GB, then set your connection speed and its unit. The calculator converts everything to bytes, applies the correct bits-or-bytes arithmetic, and shows the download time as hours, minutes and seconds, with the raw total in seconds beneath it. It recalculates as you type, and nothing is uploaded anywhere. Read the figure as a best case, one that a real transfer falls a little short of for reasons the sections below spell out.

How the estimate is calculated

A download time is data divided by rate, once both sit in matching units. The file is turned into bytes and the speed into bytes per second:

seconds = bytes ÷ bytes per second

When speed is quoted in megabits (Mbps), each byte holds eight bits, so the file's byte count is multiplied by 8 first:

seconds = (bytes × 8) ÷ (Mbps × 1,000,000)

Take the defaults: a 4.7 GB disc image over a 100 Mbps line. That is 4,700,000,000 bytes × 8 = 37,600,000,000 bits, divided by 100,000,000 bits per second, which comes to 376 seconds, or 6 min 16 s. Switch the speed unit to MB/s and the ×8 drops out, because megabytes per second already counts whole bytes.

Bits versus bytes, the trap in every speed test

Internet plans are sold in megabits, files are measured in megabytes, and the two differ by a factor of eight. A 100 Mbps connection moves 100 ÷ 8 = 12.5 MB every second, not 100 MB. Miss that and every estimate is wrong by 8×. The unit selector keeps the two apart: leave it on Mbps for the number your provider advertises and speed tests report, and switch to MB/s only when a download manager shows actual transfer in megabytes.

Where the bit and the byte came from

Both units carry a fixed history, and the gap between them is the reason a download needs two of them at once. The bit is a contraction of "binary digit," a name the statistician John W. Tukey set down in a Bell Labs memo in January 1947. It reached print the following year in Claude Shannon's paper "A Mathematical Theory of Communication," the work that founded information theory and measured messages in bits for the first time. Shannon credited Tukey with the word. A bit is a single yes-or-no choice, the smallest piece of information there is.

The byte arrived later and from a different problem. Werner Buchholz coined it in June 1956 while designing the IBM Stretch supercomputer, respelling "bite" deliberately so a slip of the pen could not turn the word back into "bit." Early machines grouped bits in varying sizes, and Stretch's byte was not yet fixed at eight. The eight-bit byte that everyone now assumes became the norm with the IBM System/360, announced in 1964, whose design settled a convention that later hardware inherited. Eight bits give 256 distinct values, room enough for a character set with a little to spare, which is why the byte and the stored character grew up together.

That split explains why the two units meet in every transfer. Networks count in bits because they send data serially, one signal at a time down a wire or a radio channel, so the bit is the natural unit of a transmission line and has been since the telegraph. Storage and files count in bytes because that is how memory is addressed and how text is held. A download crosses from one world into the other, and the factor of eight is the toll charged at the border.

From 300 bits per second to gigabit fibre

The speed half of the sum has climbed by a factor of millions in six decades. AT&T's Bell 101 dataset, the first commercial modem for computers, carried 110 bits per second when it went into service in 1958, and the Bell 103 that followed in the early 1960s raised that to 300 bits per second, slow enough to watch text arrive letter by letter. Consumer modems then climbed one published standard at a time: the ITU approved V.32bis at 14.4 kbps in February 1991, V.34 at 28.8 kbps in September 1994, a revised V.34 reaching 33.6 kbps in 1996, and V.90 at 56 kbps in September 1998, which pushed dial-up to the practical limit of a copper phone line. Broadband over DSL and cable broke through that ceiling, and fibre has since carried home connections into the hundreds and thousands of megabits. The arithmetic in this tool has not changed across any of it; only the speed you type has grown.

Decimal or binary, the other unit clash

A second, quieter ambiguity sits in the size figure. This calculator uses decimal units, so one megabyte is 1,000,000 bytes and one gigabyte is 1,000,000,000. That matches how drives and internet providers label capacity and speed. Computer memory, and some operating systems reporting file sizes, instead count in binary: 1,024 bytes to a "kilobyte," 1,048,576 to a "megabyte." The gap widens with scale, reaching about 7% at the gigabyte and more beyond it.

To end that confusion, the International Electrotechnical Commission defined separate binary prefixes in an amendment to standard IEC 60027-2, approved in 1998 and published in January 1999: the kibibyte of 1,024 bytes, the mebibyte and the gibibyte, with symbols KiB, MiB and GiB. Under that scheme the familiar prefixes kilo, mega and giga keep their plain decimal meaning. The binary names never took hold in everyday speech, but they explain why a disc sold as "4.7 GB" shows up as roughly 4.38 GiB in some file managers. For download timing the decimal reading is the right one, since it lines up with the megabits a line is rated in.

Why real downloads run slower

The formula gives the theoretical floor. In practice, add 5–10% for TCP overhead, encryption and protocol handshakes, plus the gap between a plan's headline rate and what the line sustains. A 100 Mbps plan often delivers 90–95 Mbps of usable throughput, and a busy server, Wi-Fi interference or a slow disk can pull it lower still. Read the result as a best case: that 376-second estimate is realistically closer to seven minutes.

What counts as a typical speed

Median broadband speeds vary widely by market, so the same 4.7 GB file finishes at very different times. Ookla's Speedtest Global Index measurements for December 2025 put the median fixed download at about 303 Mbps in the United States and 256 Mbps in Canada, with the United Kingdom on roughly 163 Mbps and Australia on much the same. Australia's figure has been moving quickly since NBN Co lifted its wholesale tiers on 14 September 2025, taking the 100 Mbps Home Fast product to 500 Mbps and the 250 Mbps Home Superfast product to 750 Mbps on eligible fibre and cable lines. Mobile 4G typically runs in the tens of megabits, while 5G can briefly beat home broadband. Enter your own measured speed rather than the plan's headline figure for the closest estimate.

Common file sizes at a glance

Times below assume a steady 100 Mbps connection with no overhead.

Frequently asked questions

How long does it take to download a 4.7 GB file?

At 100 Mbps a 4.7 GB file takes 376 seconds, or 6 min 16 s, in theory. Add 5–10% for overhead and expect closer to seven minutes in practice. On a 500 Mbps line the same file drops to about 75 seconds.

Is 100 Mbps the same as 100 MB/s?

No. 100 Mbps means 100 megabits per second, and because a byte is eight bits that equals 12.5 MB per second. A download manager showing 12 MB/s and a speed test showing 100 Mbps are describing the same connection, just in different units.

Why does my download take longer than the calculator says?

The formula assumes your line runs at its full rated speed with no losses. Real transfers give up 5–10% to protocol overhead, and shared servers, Wi-Fi and older drives cut into it further. A 100 Mbps plan often sustains only 90–95 Mbps of usable throughput.

Should I enter the speed in Mbps or MB/s?

Use Mbps for the number your internet provider advertises and speed-test sites report, since broadband is sold in megabits. Switch to MB/s only when a download manager or browser reports transfer in megabytes per second, which is usually a single or double-digit figure.