The fracture surface energy (γ) and the fracture toughness (KIc) of glass were estimated from the nominal composition by means of a simple approach to the structure at the atomic scale. The theoretical values are compared with the experimental ones, as obtained by means of self-consistent methods such as the Single Edge Pre-crack Beam (SEPB) and Chevron Notch (CN) ones, when available. A remarkable agreement is observed for ionocovalent glasses. In comparison, indentation cracking methods are found to mostly overestimate KIc by up to 50 %. In the case of metallic glasses, the theoretical values are much smaller than the experimental ones, which supports the occurrence of crack tip plasticity and shielding effect. Toughness (or ductility) is chiefly governed by the average coordination number, the bond directionality, and the atomic packing density.