A method of monitoring contact tip useful life in a welding torch includes measuring at least one of welding current (I) and welding voltage (V) of the contact tip mounted in the welding torch. Deterioration of the contact tip is quantified based on one or both of (i) a decrease of the welding current and increase of a standard deviation of the welding current (sd_I), and (ii) an increase of the welding voltage. Deterioration of the contact tip may be quantified by calculating an index of contact tip life (ITL) based on the welding current and standard deviation of the welding current and/or by calculating a reference index of contact tip life (ITL_v) based on the welding voltage.