We have developed a new and fast MATLAB algorithm for predicting absolute permeability. The developed tool relies on measuring the connectivity of pores in a given 3D microcomputed tomography rock image. An index of pore connectivity is evaluated. After a calibration step, the developed index is used to estimate permeability in a variety of rocks with challenging pore structures (e.g., complex carbonate formations). The developed algorithm was tested on sandstone and carbonate rock samples. It offers large computational and memory savings when compared with algorithms based on the lattice Boltzmann method. Permeability estimates were, in general, in good agreement with laboratory measurements and numerical simulation results.