When viewing performance metrics for a computer, you might see something like "Bytes In" or "Bytes Out".

What does this mean, and how does this related to "Upload" and "Download"?

Is it "Bytes In = Upload and Bytes Out = Download" or the reverse?

Example (Not my server) https://scoutapp.com/dashboards/share/hElEFAs8z_zCQRpou1M8Xw

  • it's certainly not the direction of your last sentence.If I was to guess that it had to be one way or the other, then "download" would be you receiving so 'in'.And upload since it would be you putting it somewhere, there4 if it has to be characterised as an in or an out,it'd be an out. You download from a website,U upload to an ftp server.And really if you're going to make a download then it won't all be one way, similarly uploading to an ftp server.So i'm not totally sure about characterising them as just in or out. Though speedtest talks of download and upload so I suppose one could/should.
    – barlop
    Apr 5, 2016 at 16:41
  • Where did you exactly find these two metrics (which program, which operating system)? Apr 5, 2016 at 17:29
  • @daniel.neumann Scout server monitoring. Example: scoutapp.com/dashboards/share/hElEFAs8z_zCQRpou1M8Xw
    – user229061
    Apr 5, 2016 at 17:45
  • inbox vs outbox
    – Ramhound
    Apr 5, 2016 at 17:51
  • Historically download and upload referred to file transfers within a hierarchical network (e.g. server-client or master-slave). Up/down-loading did not refer to receiving or sending, but rather the dissemination of information/data. E.G. you could download from a server and then download to a portable device.
    – sawdust
    Apr 5, 2016 at 20:46

3 Answers 3


The network is always considered to be the "outside", and the CPU etc. to be the "inside".

"Bytes In" is the amount of data received through that interface (i.e to your host from the network).

"Bytes Out" is the amount of data sent through that interface (from your host to the network).

Which of those you consider to be "upload" and which to be "download" depends on your view of your system - i.e. whether it is "up" or "down" from what that interface is connected to. If it's a home PC, you probably equate "In" with "download"; for a fileserver, "In" is usually called "upload".

You may also see "In" as "Rx" (i.e. Received) and "Out" as "Tx" (Transmitted), as in the output of ifconfig:

eth1: flags=4099<UP,BROADCAST,MULTICAST>  mtu 1500
        inet 192.168.x.x  netmask  broadcast 192.168.x.255
        inet6 fe80::xxxx:xxxx:xxxx  prefixlen 64  scopeid 0x20<link>
        ether xx:xx:xx:xx:xx:xx  txqueuelen 1000  (Ethernet)
        RX packets 1813934  bytes 68509518 (65.3 MiB)
        RX errors 1032120  dropped 0  overruns 0  frame 81778
        TX packets 1473055  bytes 1797493199 (1.6 GiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 699501
        device interrupt 18  


eth0      Link encap:Ethernet  HWaddr xx:xx:xx:xx:xx:xx  
          inet addr:172.20.x.x  Bcast:172.20.x.255  Mask:
          inet6 addr: fe80::xxxx:xxxx:xxxx:xxxx/64 Scope:Link
          RX packets:36387424 errors:0 dropped:0 overruns:0 frame:0
          TX packets:15636657 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:6378638797 (6.3 GB)  TX bytes:14222465675 (14.2 GB)
          Interrupt:20 Memory:e0380000-e03a0000 

(two different implementations of ifconfig; identifying details x'ed out)

Some tools (e.g. xosview) may show an aggregate of all network interfaces, i.e. total sent and received on all network interfaces. Then, the upstream/downstream terminology is unhelpful if some of the networks are "up" and some are "down".

  • 1
    "Which of those you consider to be "upload" and which to be "download" depends on your view of your system" Couldn't the same be said about "in" and "out" then? Apr 5, 2016 at 16:53
  • "Out" is always to the network, and "In" is always to the host. I don't think there's any doubt that the network is on the outside, and the mainboard is on the inside. Apr 5, 2016 at 16:59
  • 1
    @TobySpeight there are networks either side and it's all one network so saying "out is always to the network" is meaningless. I agree 'in' is towards the host, and likewise one could say out is from the host
    – barlop
    Apr 5, 2016 at 17:14
  • re where you wrote , "Which of those you consider to be "upload" and which to be "download" depends on your view of your system - i.e. whether it is "up" or "down" from what that interface is connected to." <------ isn't it the case that the internet is considered downstream and from the internet towards your host is considered upstream?
    – barlop
    Apr 5, 2016 at 17:16
  • 1
    I agree that upstream and downstream.. are equivalent to out and in, and to bytes transmitted and bytes received. respectively. But is it really equivalent to upload and download? If you upload a file to an FTP server, there is two way traffic,, it's not all out.
    – barlop
    Apr 5, 2016 at 17:20

In general (and without arguing about other possible uses and semantics):

"Upload" means you're sending, so (the majority of related) bits are going OUT.
"Download" means you're receiving, so (the majority of related) bits are coming IN.

Packets need responses (again, in general), so there will be bits of data flowing in the opposite direction to let one end know the other end received the last packet sent.


It simply means how much data you are consuming through that network.

You can calculate it into Megabytes by following calculation:

1 Megabyte = 1048576 Bytes

1 Kilobyte = 1024 Bytes

'In' means download and 'Out' means upload. 'In' would be greater than the 'Out' because there is less upload than download.


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