But how do you calculate the isoelectric point, the pi value of proteins that consists of two or more amino acids? Well, this is what we want to focus on in this life. We want to find out how to calculate the isolectric point of proteins. Now, the general rule is to follow the following two steps. In step one, we basically want to guess. We want to estimate what the PH value is at which that protein would have a net charge of zero.