Fracture toughness of six dental porcelains with leucite content ranging from 0 to 22 vol% was evaluated by indentation fracture (IF), surface crack in flexure (SCF), and single edge pre-cracked beam (SEPB) methods. The results of the IF method were similar to those of the SCF method for all the porcelains investigated. The results of the SEPB were similar to those of the other two methods only for the glassy porcelains, but for leucite-based porcelains this method resulted in higher values of K-Ic. Based on microstructure, fractographic analysis, and an additional single edge V-notched beam test, it was concluded that the pre-crack size influences the value of K-Ic for porcelains reinforced by leucite. For design and failure analysis purposes, the K-Ic determined by SCF method should be preferred, since fracture of dental restorations usually starts from small surface cracks.