Measure Website Size

Hello Everyone, i want to DDOS Attack on Website, it have not any SSL or WAF or similar protections, but only one thing i want to know is how to measure website size and how can i know how many packets is enough to Shut down website ? i know how to DDOS attack may i will use T50 or UFO BOTS.. have anyone idea how to measure ? i know i need some wbsite analysis tool but which one?

KALI LINUX 2

THANKS EVERYONE