Hi, if you visit sites without videos, images, or sound, it takes forever.
Surfing on sites with text and images, without sound or video, is an average of 46MB per hour of browsing; it can be more or less depending on the page sizes, the number of times per second you change pages... which would mean about 44 hours of browsing on average with 1GB.
For watching YouTube based on the recommended values https://support.google.com/youtube/answer/2853702?hl=en-GB
1080p:
4500 Kbps = 562.5 kB/s, 1024*1024/562.5=1969.15 seconds = 32 min
720p:
2500 Kbps = 312.5 kB/s, 1024*1024/312.5=3355.44 seconds = 55 min
480p:
1000 Kbps = 125 kB/s, 1024*1024/125=8388.6 seconds = 2 hours 19 min
360p:
750 Kbps = 93.75 kB/s, 1024*1024/93.75=11184.81 seconds = 3 hours 6 min
There is a calculator here http://www.virginmobile.ca/fr/support/data-support.html