By Looking at it you will only know its maximum according to specs of the specific Network Adapter. You have to look up the specs.
For actual speed it would need to be measured using a utility. If wanting to measure speed of computer on the internet for upload/download average you can go to
www.speedtest.net If you have a group of computers that are 100mbps and you have a 10mbps hub then your capped at a 10mbps connection because of the hub bottleneck. Then you also have to deal with network congestion and so even if you had computers all 100mbps connected thru a 100mbps switch, depending on what traffic other systems have on this same network it will slow down and speed up towards maximum speed as multiple systems compete for bandwidth. *Note: Some network adapters show a Green or Yellow LED indicating speed, but not all network adapters have this feature. Some older ones even have a 10/100 or 100/1000 with individual LEDs lit to indicate the speed at which its handshaking with the switch or other computer over a cross over cable etc.
Then the other bottleneck is your ISP connection you can have a computer with a 1000mbps connection to your modem, but have a 1.2mbps internet connection.
