Press the Calculate button to calculate the sample size.
The required number of events and the power for the logrank test are calculated according to Schoenfeld's formula, see [Schoenfeld, D. (1981). The asymptotic properties of nonparametric tests for comparing survival distributions. Biometrika, 68(1), 316-319.] and [Schoenfeld, D. A. (1983). Sample-size formula for the proportional-hazards regression model. Biometrics, 499-503.]