2

When I run a test on speedtest.net, I get 90Mbps for download and 35Mbps for upload.

Looking at Activity Monitor I see 50 MB/s and 17.5MB/s.

My understanding is that 1Mbps equals 0.125MB/s.

Why is there a discrepancy?

  • How do you get Activity Monitor to show transmission in MB/s? I don't see that. The answer is probably that they use different averaging, but I can't test. – Tetsujin Nov 19 at 12:17
  • @Tetsujin In Activity Monitor (Catalina), in the Network tab, bottom right... Data sent and received/sec in KB or MB (adjusted to current throughput). – sunknudsen Nov 19 at 12:20
  • Ah, yup, found it. Yes, it's using totally different averaging method. It's not examining the exact start & stop point that Speedtest is, it's just doing an average over the past perhaps 5 seconds. I got 217mbps Speedtest, 20MB/s Activity Monitor. It took it at least 2 updates to even reach that, by which time Speedtest had just about finished. – Tetsujin Nov 19 at 12:24
3

It's using a totally different averaging method.
It's not examining the exact start & stop point that Speedtest is, it's just doing an average over the past 5 seconds.

I got 217mbps Speedtest, 20MB/s Activity Monitor. It took it at least 2 updates to even reach that, by which time Speedtest had just about finished.

Switching Activity Monitor from its default 5 second update to just 1 second* & the values just about match - I was getting 217mbps Speedtest with 27MB/s Activity Monitor (roughly).

Also bear in mind you are comparing a one-trick pony - an app dedicated to providing line speed results - against one that's more a general overview of what your entire machine is doing.

After comments
As there was still a discrepancy at 1s sampling, try to eliminate sources of error - switch from WiFi to wired Ethernet; remove any VPN connections; test another account or Mac.

*View menu > Update Frequency

| improve this answer | |
  • Thanks! What about the 17.5MB/s vs 35Mbps? My connection cannot go faster than 40Mbps upstream... Wouldn't 17.5MB/s equate to 140Mbps? – sunknudsen Nov 19 at 12:27
  • 1
    Test it again on a 1s update – Tetsujin Nov 19 at 12:28
  • Done... Somehow speeds in Activity Monitor appear to be half of what they are on speedtest.net. I don't understand the maths. Do you know why? Btw speeds are reported correctly in MB/s by Little Snitch. – sunknudsen Nov 19 at 12:32
  • I can't explain that discrepancy. Mine matches (approximately) in both directions. If you're on wifi, wire up to eliminate that as the cause. – Tetsujin Nov 19 at 12:35
  • As mentioned, Little Snitch reports the speeds accurately so it isn't a Wi-Fi issue... perhaps it's a VPN issue though. Now I know it's specific to my setup. Thanks for your help! – sunknudsen Nov 19 at 13:17

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .