Apdex is an industry standard for measuring user satisfaction through the response time of a server or a site. You’ll be able to fix the threshold time ‘T’ from which apdex is calculated.

There are three states in customer satisfaction
Response time < T; satisfied
Response Time = T; Tolerating
Response Time > 4T; Frustrated
Apdex is calculated using the formula
Apdex = ((satisfied Requests) + (Tolerating Requests/2)) / Total number of requests
Example: For example, if T is 1.2 seconds and a response completes in 0.5 seconds, then the user is satisfied. All responses greater than 1.2 seconds dissatisfy the user. Responses greater than 4.8 seconds frustrate the user.