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Internet speed vs download speed: why 100 Mbps shows 12.5 MB/s

Internet speed vs download speed: why 100 Mbps shows 12.5 MB/s

Internet plans are sold in megabits per second, and download windows count megabytes per second. Convert one to the other, work out how long a file should take, and size a connection for a month of traffic.

internet speed vs download speed By · Updated

Bits on the plan, bytes in the download window

An internet plan is measured in bits: Mbps, megabits per second, with a lowercase b. A browser or download manager usually shows bytes: MB/s, megabytes per second, with a capital B. One byte is 8 bits, so the plan figure is 8 times the download figure for the same speed. A 100 Mbps plan moves at most 12.5 MB/s. A 1 Gbps plan moves at most 125 MB/s. If you pay for 100 and the screen says 12.5, the difference is the unit.

A second gap comes from the label. Some download managers show binary MiB/s and still call it "MB/s". That makes the same speed look about 5% lower again, so 100 Mbps appears as 11.92 instead of 12.5.

The rest is real loss. The plan speed is a maximum. Protocol overhead, Wi-Fi quality, a busy network, and the limits of the server on the other end all bring the actual rate down. The same words also mean two things in hosting. Bandwidth is a rate, such as 100 Mbps. Data transfer is a volume, such as 500 GB in a month, and many hosting plans call that monthly volume "bandwidth" too.

Convert the speed, time the file, then size the month

Use the Mbps to MB/s Converter first. Enter the value, pick its unit (Kbps, Mbps, Gbps, KB/s, MB/s, GB/s, or MiB/s), and press Convert. A bit-based unit gives MB/s as the main result, a byte-based unit gives Mbps, and every other unit is listed underneath. Swap reverses the direction. The page's own figures: 100 Mbps is 12.5 MB/s or 11.92 MiB/s, 1 Gbps is 125 MB/s, and 50 MB/s is 400 Mbps. A negative value is an error. These are ideal rates before network overhead.

To see what that speed means for one file, use the Download Time Calculator. Enter the file size with its unit, such as GB or GiB, and the speed with its unit. The time is the size in bytes times 8, divided by the speed in bits per second. Tick Include network overhead to take 10% off the speed, and raise it as far as 50% if your line is worse. At 100 Mbps, 1 GB takes 80 seconds and 5 GB takes 6 min 40 s, or 7 min 24 s with 10% overhead. 50 GB at 25 Mbps takes 4 h 26 min 40 s. The calculator assumes the speed stays constant, so the answer is a best case. A speed of 0 is an error.

For a website or a hosting plan, open the Bandwidth Calculator. Data rate mode gives the speed a volume needs: 10 GB every hour needs 22.22 Mbps sustained. Website mode multiplies page views by the average page size and a redundancy factor, 1.5 by default, for peaks, crawlers, and repeat visits: 100,000 views of a 2 MB page is 300 GB a month, an average of 0.93 Mbps. Hosting mode converts monthly transfer to a speed and back: 1 TB a month is 3.09 Mbps sustained, and a 100 Mbps port used around the clock moves 32.4 TB in 30 days. A month here is 30 days. KB, MB, GB, and TB are powers of 1,000, and KiB, MiB, GiB, and TiB are powers of 1,024.

Turn a plan speed into download times and monthly traffic

  1. Enter your plan speed in Mbps in the Mbps to MB/s Converter and note the MB/s figure. That is the fastest a download can show.
  2. If your download manager reports a lower number, check whether it shows MiB/s under a "MB/s" label. The converter lists both.
  3. Enter the file size and the plan speed in the Download Time Calculator. Turn on network overhead for a closer estimate.
  4. For a site or a server, choose Website or Hosting in the Bandwidth Calculator and enter page views and page size, or the monthly transfer from the plan.
  5. Size the connection for busy hours rather than the monthly average, and leave room for the 10 to 20% that protocol overhead takes.

What the three calculators assume

  • Every result is an ideal rate or a best-case time. Wi-Fi, congestion, server limits, and the gap between peak and sustained speed are not measured.
  • The download time assumes one constant speed for the whole file. Overhead is a percentage you choose, not a measurement.
  • Bandwidth figures are averages over a 30-day month. Traffic peaks are higher, and protocol overhead is not included.
  • Hosts that bill 95th-percentile usage instead of total transfer are not modeled.

Frequently asked questions

Is 100 Mbps the same as 100 MB/s?

No. Mbps is megabits and MB/s is megabytes, and one byte is 8 bits. 100 Mbps is 12.5 MB/s at most.

How long does a 1 GB download take on a 100 Mbps connection?

About 80 seconds in ideal conditions: 1 GB is 8,000 megabits, and 8,000 divided by 100 is 80. Overhead and Wi-Fi make it longer.

Why does my download manager show less than the converter?

Some programs show MiB/s but label it MB/s, which reads about 5% lower. Overhead, Wi-Fi, congestion, and server limits take more off the real speed.

How many GB a month can a 1 Mbps line carry?

About 324 GB in a 30-day month if it runs at full speed the whole time: 1,000,000 bits times 2,592,000 seconds, divided by 8.

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