Since a recent update to chrome, the presets are no longer labelled with bandwidth.
Chrome used to list the actual speed of each one so you could simply tell.
W
Here is a csv of the values in the screenshot from Robroi2000's answer
Preset,download(kb/s),upload(kb/s),RTT(ms) GPRS,50,20,500 Regular 2G,250,50,300 Good 2G,450,150,150 Regular 3G,750,250,100 Good 3G, 1000,750,40 Regular 4G, 4000,3000,20 DSL 2000, 1000,5 WiFi 30000,150000,2