Android : Performance of online android application based on response and network based on number of users

i have developed a simple online android application that download image from a given URL. The next task is to test the application based on many users and i have already calculated the response time (R) and the network speed (L), that is the speed at which the image is downloaded. The number of users is given as N. The users can be considered as Virtual users. Is there any way to use these three metrics to calculate the performance or load of the application as an unit of 0 to 100 %? The equation should be in the format below:

performance % = f(R, L, N)

This way by increasing the number of users from 1,2,3...10, the performance of the application can be analyzed...but im not sure if this formulation is possible...need some suggestions please..

The response time is in milliseconds and network speed is KBps..