From the antlers of deer to the claws of crustaceans, animal weapons exhibit a diversity of shapes and sizes. Some of this diversity might stem from the selective pressures imposed on the weapons from fighting. However, two problems arise when considering that assumption. First, evidence that weapons increase fight success focuses on studies with few species. Second, how weapons are measured vary; while some studies focus on size estimates, others focus on performance components (e.g., strength). To address these concerns, we performed a meta-analysis to compare standardized estimates of how weapons can influence contest success. After scanning 1108 papers and 12 relevant reviews, we totaled 107 effect sizes from 51 species of vertebrates and invertebrates. In these studies, 69.15% (74 out of 107) reported linear estimates of size, while 21.49% (23) reported performance estimates. Interestingly, we found performance estimates mainly for crustaceans and lizards, with only one estimate in crickets. For the effect of weapon size on contests, we used the standardized difference between winners and losers as our effect size; it has been shown that larger differences in a given trait indicate higher contest success. We found that winner and losers differed significantly for size estimates, but found only marginal difference for performance estimates. Additionally, linear estimates had larger differences between winners and losers than performance estimates. Our results thus suggest that size is more important for contest success than performance. However, they also suggest strong biases in the literature, which prevents further understanding of how different proxies can influence weapon evolution and diversification.