What is the reference value of standard deviation of white Gaussian noise when doing SINR simulation?

Hi! what is the standard deviation of white Gaussian noise when doing SINR simulation?

I am new to communication simulation. I have a project which needs to calculate SINR. SINR = P/(N+I), and here the noise is white Gaussian noise. Generally speaking, is there any reference value of standard deviation of white Gaussian noise?

Any comments or leads are welcome. Thanks in advance for your kind help.