1. Network Utility.
2. System Information.
3. Wireless Network Preferences Menu Bar Icon Shortcut.
4. airport Command Line Utility.

Method #1: Checking the wireless connection speed using network utility

First, click on Spotlight and type “network utility“. OR press command + space-bar and type “network utility“.

Make sure you select network utility. Select Info tab and choose Wi-fi (en0 or en1) on the drop-down options. Please note that the Link Speed is your wireless connection speed. In this example, my connection speed is set to 450 Mbit/s (Mega bits per seconds).

Method #2: Checking the wireless connection speed using system information

Click on Spotlight and tye “system information“. OR press cmd+space-bar and then type “system information“. Finally, choose Network and select Wi-Fi. The WI-FI connection information will be displayed on the right.

Method #3: Finding wireless status using option key

1. First, hold down the Option key.
2. Next, Click on Wireless icon (Airport icon) and you will see information as follows:

Method #4: Command line utility

Open a terminal. Type the following command:

/System/Library/PrivateFrameworks/Apple80211.framework/Versions/Current/Resources/airport -I

Sample outputs:

     agrCtlRSSI: -62
     agrExtRSSI: 0
    agrCtlNoise: -86
    agrExtNoise: 0
          state: running
        op mode: station 
     lastTxRate: 150
        maxRate: 450
lastAssocStatus: 0
    802.11 auth: open
      link auth: wpa2-psk
          BSSID: 50:46:5d:d2:36:8c
           SSID: very5_G
            MCS: 7
        channel: 161,-1

I strongly recommend that you use network utility for ease of use.