Bits and bytes: the eight-times difference

Internet providers and speed tests measure in megabits per second, written Mbps or Mb/s with a small b. Browsers, game launchers and file sizes use megabytes, written MB with a capital B. One byte equals eight bits.

So a 100 Mbps connection transfers at most about 12.5 MB per second. When a download shows 11 MB/s on a 100 Mbps plan, your connection is performing well, not badly.

The same applies at higher speeds: a gigabit plan, 1,000 Mbps, tops out at about 125 MB/s before overhead.

Quick conversions

Divide Mbps by 8 to get MB/s. Multiply MB/s by 8 to get Mbps. In practice, expect about 5 to 10 percent less because of network protocol overhead.

Storage makers and operating systems also disagree on whether a gigabyte is 1,000 or 1,024 megabytes, which adds a few more percent of confusion.

  • 25 Mbps ≈ 3.1 MB/s
  • 50 Mbps ≈ 6.3 MB/s
  • 100 Mbps ≈ 12.5 MB/s
  • 300 Mbps ≈ 37.5 MB/s
  • 500 Mbps ≈ 62.5 MB/s
  • 1 Gbps ≈ 125 MB/s

How long should a download take?

Convert the file size to megabits, then divide by your speed. A 50 GB game is 50,000 MB, or 400,000 megabits. At 100 Mbps that is 4,000 seconds, a little over an hour. At 1 Gbps it is under seven minutes in theory.

Real downloads are often slower because the server limits speed per user, Wi-Fi is slower than the plan, or other devices share the connection.

Estimate download time
Time (seconds) ≈ (File size in MB × 8) ÷ Speed in Mbps

4 GB movie at 50 Mbps:   (4000 × 8) ÷ 50   = 640 s  ≈ 11 min
50 GB game at 300 Mbps:  (50000 × 8) ÷ 300 = 1333 s ≈ 22 min

Why downloads can be slower than your speed test

A speed test measures the path to a nearby test server, often with several parallel connections. A single download from a distant or busy server can be much slower. Some services also cap download speed per user during busy periods.

Wi-Fi is the next suspect: run a speed test on the same device and network as the download. Disk speed rarely matters on modern computers, but old hard drives and SD cards can limit very fast downloads.

If both the speed test and downloads are slow, see our guide to why your internet may be slow.

Upload works the same way

Upload speeds use the same units. A 20 Mbps upload sends about 2.5 MB per second, so backing up 10 GB of photos takes a little over an hour at full speed.

Upload is often much lower than download on cable and DSL plans, which is why cloud backups and video uploads take longer than downloads of the same size.

Run a speed test to see both numbers for your connection, then use them in the formula above.