How should I calculate Ramp-up time in Jmeter

Question

There are many questions/answers available here to understand Ramp up time but I want to get something in detail for my test case.

Test Case

Answer 1

Rampup is the speed at which users arrive on your application. The number you put means that once it is reached all threads have been started. The tiniest it is , the faster users arrive. So nobody can answer that for you, you need to analyse your traffic.

Regarding the number of threads, 1200 threads might not be the good number, as 1200 users can navigate on application slowly or rapidly. What you need is add a Constant Throughput Timer to control how much transactions per second you'll be reaching.