| Megabits per second (Mbit/s) | Exabits per second (Ebit/s) |
|---|---|
| 1 Megabit per second | 1 × 10-12 Ebit/s |
| 2 Megabits per second | 2 × 10-12 Ebit/s |
| 3 Megabits per second | 3 × 10-12 Ebit/s |
| 4 Megabits per second | 4 × 10-12 Ebit/s |
| 5 Megabits per second | 5 × 10-12 Ebit/s |
| 10 Megabits per second | 1 × 10-11 Ebit/s |
| 20 Megabits per second | 2 × 10-11 Ebit/s |
| 25 Megabits per second | 2.5 × 10-11 Ebit/s |
| 50 Megabits per second | 5 × 10-11 Ebit/s |
| 100 Megabits per second | 1 × 10-10 Ebit/s |
| Reference | Megabits per second (Mbit/s) | Exabits per second (Ebit/s) |
|---|---|---|
| A dial-up modem | 0.056 Mbit/s | 5.6 × 10-14 Ebit/s |
| Typical home broadband | 100 Mbit/s | 1 × 10-10 Ebit/s |
| Gigabit Ethernet | 1000 Mbit/s | 0.000000001 Ebit/s |
| Streaming a 4K film | 25 Mbit/s | 2.5 × 10-11 Ebit/s |
The megabit per second is a unit of data transfer rate equal to one million bits per second. Its symbol is Mbit/s, often written Mbps. It is the unit in which internet connections are sold, which makes it the data unit most people encounter by name.
Because it is a decimal million and not 1,048,576, the conversion to octets is exact and easy: one megabit per second is 125 kilooctets per second, so a hundred-megabit connection delivers about 12.5 megaoctets per second at best. Anyone who watches a file transfer and does the division has understood the entire relationship between how connections are advertised and how transfers are reported.
What a household actually needs is far below what it usually buys. Standard-definition video streaming uses about 3 megabits per second, high definition about 5, and ultra-high definition about 25. A video call is around 3 to 8. A large family watching four separate high-definition streams while somebody downloads a game is using perhaps 60 megabits per second, which a hundred-megabit connection handles comfortably.
The reason to buy more capacity than that is not peak speed but behaviour under load. A link that is near its limit develops queues, and queues add delay, which shows up as stutter in video calls and lag in games. A connection with generous headroom keeps its latency low, and that is a more noticeable improvement than a higher number on a speed test.
Wired local networks pass through this range on the way up. The original Ethernet ran at 10 megabits per second, its successor at 100, and both were the standard office connection for a decade each before gigabit replaced them. Wireless standards followed the same path with a lag, and both are now measured in hundreds of megabits or in gigabits.
Real throughput is always below the nominal rate. Protocol overhead takes 5 to 10 per cent on a wired link; a shared wireless channel loses much more, because the medium is divided between all the devices using it and interference forces retransmission. A connection advertised at 100 megabits per second measured at 90 over cable and 50 over a busy wireless network is behaving normally.
One megabit per second equals 1,000,000 bits per second, 125 kilooctets per second, or about 0.9537 mebibits per second.
The exabit per second is a unit of data transfer rate equal to a thousand petabits per second. Its symbol is Ebit/s. No link, no cable and no exchange point runs at this rate; the unit describes the internet as a whole, or a large part of it, at a single instant.
Global internet traffic can be expressed this way. Worldwide traffic of several hundred exaoctets a month works out to roughly one exabit per second on average, and peak hours run higher. That figure is the sum of every packet moving on every network on the planet, and it is the only quantity anyone routinely describes at this scale.
An exabit per second is 125 petaoctets per second. Nothing generates data at that rate in one place; the number is an aggregate of billions of separate flows, most of them tiny. A single video stream is a few megabits per second, so an exabit per second is on the order of a hundred million such streams running at once.
The composition of that traffic is dominated by video. Streaming services account for the largest share, followed by social platforms, software updates and cloud synchronisation. Ordinary web browsing and messaging, which people think of as the internet, are a small fraction of the total by volume even though they occupy most of the attention.
The unit also appears in projections of aggregate capacity. The total installed capacity of all submarine cables, if every wavelength on every fibre pair were lit and used simultaneously, is in the exabit-per-second range. Actual utilisation is far below that, because capacity is built ahead of demand and because routes must carry each other's traffic when a cable fails.
The prefix exa is a thousand to the sixth power. It was adopted in 1975, when nobody expected it to describe anything but astronomical quantities, and it now describes the working throughput of a communications system built by human beings. The interval between definition and everyday use was about forty years.
One exabit per second equals 1,000 petabits per second, 125 petaoctets per second, or about 0.8674 exbibits per second.