"it shows" - where? Sounds like the hardware interface range. That's theoretical, generally not achieved.
Internet speed and WiFi speed are 2 different things. Internet speed is normally the speed of your cable or other modem. WiFi speed is the speed of data transfers between devices in your network, generally depends on the speed of your router. Because of WiFi overhead it would be exceptional to get 900 Mbps. If you are getting 40 MB/s thats 320 Mbps which is actually a rather good WiFi result depending on location, interference, distance, etc.
You can measure your WiFi network speed by running programs such as network speed tester on two devices on your network. One serves as a server, the other as a client.