The mathematical formulation for estimating phasors from phasorlets, obtained from signal segments of a fraction of a cycle, is established and the frequency responses of the phasorlet generator filters are evaluated. From the theory and the numerical simulations it is concluded that, when the signal segment involved in the phasorlet generation corresponds to a pure sinusoidal signal, this estimation technique offers the quickest measurement of its phasor, improving the speed of the well known one-cycle Fourier filter estimate. The new estimates were found very useful for detecting and locating abrupt changes in amplitude or phase between two sinusoidal states. However, before transients or impure sinusoids, the exactness and the dynamic behavior of this estimation method (which includes the one-cycle Fourier filter) will depend in great extent on the applied noise extraction technique, given the huge sensitivity to nonsinusoidal signals of the phasorlet generator filters.