When referencing the F distribution, the numerator degrees of freedom are always given first, as switching the order of degrees of freedom changes the distribution (e.g., F (10,12) does not equal F (12,10)). For the four F tables below, the rows represent denominator degrees of freedom and the columns represent numerator degrees of freedom. How to Use a Critical F-Values Calculator? First of all, here you have some more information about critical values for the F distribution probability: Critical values are points at the tail(s) of a certain distribution so that the area under the curve for those points to the tails is equal to the given value of \(\alpha\).Therefore, for a two-tailed case, the critical values correspond to two Computes p-values and F values for the Fisher-Snedecor distribution. StatDistributions.com - F-distribution calculator Enter either the p-value (represented by the blue area on the graph) or the test statistic (the coordinate along the horizontal axis) below to have the other value computed.