DF means degrees of freedom
Use the sample size minus the number of estimated parameters
For a one-sample mean: DF = n – 1
For an independent two-sample t-test: DF = n1 + n2 – 2
For a paired t-test: DF = n – 1
For a chi-square goodness-of-fit test: DF = k – 1 – p
For a chi-square test of independence: DF = (r – 1)(c – 1)
For one-way ANOVA: DF between = k – 1
For one-way ANOVA: DF within = N – k
For one-way ANOVA: DF total = N – 1
For linear regression: DF for model = number of predictors
For linear regression: DF for error = n – p – 1
For linear regression: DF total = n – 1