The logit function is the inverse of the sigmoidal 'logistic' function or logistic transform in statistics. It gives the log-odds, or the logarithm of the odds in statistical data. The logit function is a canonical link function for the Bernoulli distribution in generalized linear model. It is just the negative of the derivate of the binary entropy function. Use the below online logit calculator to find the logit evaluation value for the given proportion.
Find Logit with p = 0.8= loge(0.8 / 1- 0.8))