Basic methods to compute required sample sizes are well understood and supported by widely available software. However, the sophistication of the methods commonly used has not kept pace with the complexity of commonly employed experimental designs. We compile available methods for sample size calculations for continuous and binary outcomes with and without covariates, for both clustered and non-clustered RCTs. Formulae for both panel data and unbalanced designs are provided. Extensions include methods to: (1) optimise the sample when costs constraints are binding, (2) compute the power of a complex design by simulation, and (3) adjust calculations for multiple testing.