Glossary/Figures Activity Monitor leaves out
Mbps and MB/s
Also: megabits and megabytes per second
Quick answer
Mbps is megabits per second and MB/s is megabytes per second. A byte is eight bits, so 100 Mbps is 12.5 MB/s. Internet plans and speed tests use bits; Activity Monitor, Finder and the download bar in a browser use bytes, which is why a fast connection looks slow in Activity Monitor.
The two units measure the same thing and differ only by a factor of eight, plus the capital letter that tells them apart: a small b is bits, a big B is bytes. A 1 Gbps fibre connection tops out at 125 MB/s in Activity Monitor's Network tab. A 500 Mbps plan is 62.5 MB/s, and a download running at 60 MB/s is using nearly all of it.
The habit of quoting network speed in bits is older than the personal computer and is not going away, so the conversion is worth keeping in your head: divide bits by eight to get bytes, or multiply bytes by eight to compare with your plan.
Which unit each Mac tool uses
Activity Monitor's Network tab shows Data received/sec and Data sent/sec in bytes, from KB/s to MB/s, and the totals below it in bytes too. Finder's copy dialog and Safari's download list show bytes per second. Speed tests, the Wi-Fi details in System Settings, and your internet provider quote bits: Mbps or Gbps.
Wi-Fi link speed is a third thing again. The Tx Rate in the Wi-Fi menu (hold Option and click it) is the rate the radio negotiated, in Mbps, and real transfers reach about half of it.
- Activity Monitor, Finder, browsers: bytes (KB/s, MB/s).
- Speed tests, internet plans, Wi-Fi link speed: bits (Mbps, Gbps).
- To compare: bytes × 8 = bits, or bits ÷ 8 = bytes.
Checking whether a download is as fast as it should be
Take the plan's speed in Mbps and divide by eight. That is the ceiling in MB/s that Activity Monitor can show. A 300 Mbps plan cannot show more than 37.5 MB/s, and a download at 30 MB/s is doing well. Below a quarter of the ceiling, the bottleneck is elsewhere: the server, Wi-Fi, or another app using the connection.
Questions people ask
Is Activity Monitor showing Mbps or MB/s?
Megabytes per second. Activity Monitor's Network tab counts in bytes. Multiply by eight to compare with your internet plan, which is quoted in megabits.
How many MB/s is 100 Mbps?
12.5 MB/s. Divide megabits by eight to get megabytes. 1 Gbps is 125 MB/s.
Why is my download slower than my internet speed?
Often it is not: a 200 Mbps plan is 25 MB/s, and a download showing 22 MB/s is using nearly all of it. If it really is slower, the server or the Wi-Fi is the limit, or another app is sharing the connection.
Related
Want to watch this all the time? See the best system monitors for Mac, or the best Activity Monitor alternatives. Or browse every term in the glossary.