Approximate formulas for the calculation of the output voltage, ripple voltage, and the r.m.s. and peak values of the source current of bridge, and one- and two-phase halfwave rectifier circuits are presented. These have been derived by replacing sines and cosines by the first two terms of their series expansions. It is shown that the approximations made introduce errors which, in the great majority of practical applications, are less than 1%. Brief comments on the practical application of the formulas are made, and some calculated and measured values of the output and ripple voltages presented, showing good agreement.