The strength of elastomers can be successfully described utilising a fracture mechanics approach adopting a tearing energy concept. This was originally developed using an energy balance approach which for some geometries allows us to ignore the detailed complex stress field ahead of an advancing crack tip. Preliminary research work by A.G. Thomas considered the complex stress and strain field ahead of advancing crack tip where it was proposed that the tearing energy can also be derived from the elastic stored energy ahead of crack tip acting over the effective crack tip diameter. However, this work has not been extensively extended.This work attempts to elucidate the strength of elastomers with specific crack tip diameters by considering their behaviour using both conventional tearing energy and effective crack tip diameter approaches. The measured tearing energy is the combination of intrinsic fracture toughness of the elastomer compound and its effective crack tip diameter. This approach allows both of these factors to be determined independently. It was found that there is large impact of mechanical shape factor originating from the nature of elastomer compound and its morphology on the crack growth resistance, especially at relatively low tearing energy values. It is well known that butadiene rubber blended elastomer compounds exhibit superior cyclic crack growth resistance despite the critical tearing energy being lower as the volume fraction of butadiene rubber increases. It can be concluded that the origin of its superior cyclic crack growth resistance results from an increase in the effective tip diameter encountered in these elastomer compounds.The theoretical background about how these detailed methodologies can be used to investigate the intrinsic fracture toughness ahead of an advancing crack tip and mechanical shape factor are reported in this paper.