Bandwidth Calculator

Enter a speed, choose whether it is quoted in megabits per second, megabytes per second, or gigabits per second, and the calculator returns all three forms together with the volume of data the link would move in an hour and in a day at full tilt. The result recalculates as you type. It settles the question every broadband shopper reaches sooner or later: the plan says 500 Mbps, so what does that translate to for a file actually landing on the disk?

Bits, bytes, and the factor of eight

Telecom links have been rated in bits per second since the telegraph era, and providers stay with that convention partly because the figure reads larger — a 500 Mbps plan sounds faster than the identical line described as 62.5 MB/s. A byte is eight bits, so moving between the two is a single division:

MB/s = Mbps ÷ 8

Downloads, file sizes, and progress bars are nearly always shown in bytes, which is why a 500 Mbps connection tops out near 62 MB/s in your browser rather than the 500 the label suggests. Nothing has been lost. The two numbers describe the same line measured against different units, and the factor of eight between them is fixed.

Where these units came from

The bit is younger than it feels. The word is a contraction of "binary digit," and it reached print in Claude Shannon's 1948 paper "A Mathematical Theory of Communication," the founding document of information theory. Shannon credited the coinage to his Bell Labs colleague John Tukey, who had used it in an internal memo dated 9 January 1947. The byte followed in 1956, when Werner Buchholz coined it during the early design work on the IBM 7030 Stretch supercomputer, respelling "bite" so it would not be mistaken for "bit." Early bytes were not fixed at eight bits at all; the eight-bit byte became the settled standard with the IBM System/360, announced in 1964, and has stayed there since.

Baud and bandwidth carry longer histories still. Baud, the count of signalling events per second, is named for the French telegraph engineer Émile Baudot, whose five-unit code, devised in 1870 and patented in 1874, let a single line carry the alphabet; the unit itself was adopted by the international telegraph consultative committee in November 1926, more than twenty years after Baudot's death. Bandwidth began as a frequency term — the width, in hertz, of the band of frequencies a channel can carry. In papers published in 1928, two engineers of the Bell System, Harry Nyquist at AT&T and Ralph Hartley at Bell Telephone Laboratories, worked out how that frequency width caps the number of symbols a channel can pass each second, the root of the modern habit of calling a data rate a bandwidth even when no frequencies are named. When AT&T shipped the Bell 103 modem in 1962 at 300 bits per second, one bit equalled one baud; later modems packed several bits into each symbol, and the two counts parted ways.

What an hour at full speed actually moves

Saturate the line and the totals mount quickly. Multiply bytes per second by the seconds in an hour, then convert to gigabytes:

GB/hour = MB/s × 3600 ÷ 1000

Take the default 500 Mbps. Dividing by eight gives 62.5 MB/s. Over an hour that is 62.5 × 3600 = 225,000 MB, or 225 GB. Hold it flat out for a full day and 225 × 24 = 5,400 GB, which is 5.4 TB. Almost no connection sustains that — it assumes zero overhead and no competing traffic — but it sets the ceiling. On a metered or capped plan, an hour of maxed-out downloading can swallow a large share of the month's allowance.

The overhead that trims the last few percent

The divide-by-eight figure is a theoretical peak, and real transfers land a little below it. Every payload is wrapped in headers by the Ethernet, IP, and TCP layers, and the connection also spends capacity on acknowledgements, retransmitted packets, and encryption handshakes. The arithmetic is easy to pin down at the Ethernet layer: with the usual 1,500-byte maximum transmission unit, a full frame carries 1,460 bytes of TCP payload once the 20-byte IPv4 and 20-byte TCP headers are subtracted, while the wire spends the equivalent of 1,538 bytes on that frame after framing, checksum, preamble, and the gap before the next one. That is close to 95 percent efficiency before anything else goes wrong, so a healthy link usually delivers a few percent under its nominal rate. On the default 500 Mbps line, a sustained 55 to 62 MB/s is normal rather than a sign of anything wrong; the shortfall is the protocol doing its job, not the carrier underdelivering.

Decimal or binary: the 1,000 versus 1,024 question

Networks count in powers of ten. A kilobit is 1,000 bits, a megabit is 1,000,000, and the calculator treats 1 GB as 1,000 MB throughout. Memory chips and many operating systems instead count in powers of two, where a kilobyte has historically meant 1,024 bytes and a gigabyte 1,073,741,824. The gap is minor at kilobyte scale but compounds upward: a decimal gigabyte is about seven percent smaller than a binary one and a decimal terabyte about nine percent smaller, which is why a drive sold as 1 TB reports as roughly 931 GiB. To end the ambiguity the International Electrotechnical Commission introduced binary prefixes in 1998 — kibi, mebi, and gibi, with the symbols KiB, MiB, and GiB — reserving kilo, mega, and giga for the decimal values. Carriers meter traffic in the decimal units, so the per-hour and per-day figures here match the numbers on the bill rather than the binary ones a file manager may show.

What everyday use actually demands

The ceiling is worth putting in perspective. Streaming standard-definition video needs only a few Mbps; a high-definition stream sits around 5 Mbps; the major 4K services commonly recommend 15 Mbps or more; a one-to-one video call runs on a few Mbps in each direction. A single 500 Mbps line can therefore carry many of those at once, which is why the headline number matters less for one device than for a household sharing the pipe. The per-hour total is the more telling figure on a capped plan, since an evening of 4K streaming at roughly 7 GB an hour, or one large game download, can move tens of gigabytes without the connection ever approaching its rated speed.

Why speed tests never sit still

Run a speed test twice and you rarely get the same reading. Wi-Fi interference, the distance to the test server, congestion in the peak evening hours, and TCP ramp-up can each move the reading by ten percent or more from one run to the next. That variability is why advertising rules increasingly demand typical rather than best-case figures. In the UK, an ASA standard in force since May 2018 requires any headline speed in an advert to be a median available to at least half of customers during the 8pm to 10pm peak, and to be described as an average. The EU's net-neutrality regulation, 2015/2120, requires fixed-line contracts to state minimum, normally available, maximum, and advertised download and upload speeds. Australia's ACCC promotes a typical busy-period label based on the 7pm to 11pm evening window, and the US FCC has required broadband consumer labels listing typical download speed, upload speed, and latency since April 2024. Because this calculator works in the decimal convention networks run on, its output lines up with the units a carrier bills against rather than the binary ones your file manager may display.

Frequently asked questions

Why is my 500 Mbps connection only downloading at 60 MB per second?

Your plan is quoted in megabits and downloads are measured in megabytes, and there are 8 bits in a byte. 500 Mbps divided by 8 is 62.5 MB/s, so a real figure of 55 to 62 MB/s is exactly what you should expect. The apparent slowdown is a unit change, not lost speed, though protocol overhead trims a few percent off the theoretical peak.

How many GB does an hour of downloading use at 100 Mbps?

At 100 Mbps you move 12.5 MB every second, which is 45 GB over an hour of continuous transfer. Run that for a full day and it reaches 1.08 TB. Most links never sustain their peak for long, so treat these as ceilings rather than typical usage.

What is the difference between Mbps and MB/s?

Mbps is megabits per second and MB/s is megabytes per second, and one byte is 8 bits, so MB/s is always Mbps divided by 8. A 1,000 Mbps gigabit line therefore peaks at 125 MB/s. Providers quote the bit figure because it is eight times larger and reads faster on the marketing page.

Is a gigabit connection the same as 1,000 Mbps?

Yes. Gigabit means 1 Gbps, which is 1,000 Mbps or 125 MB/s under the decimal convention networks use. A saturated gigabit link moves 450 GB in an hour and 10.8 TB in a day, though shared infrastructure and Wi-Fi rarely let a home connection reach that.