The effective population size (Ne) is crucial for predicting inbreeding and genetic variation loss in wildlife. Since only census population size (N) is typically available, the ratio Ne/N is essential for evolutionary genetics and wildlife management. A review of 192 estimates from 102 species identified key variables affecting Ne/N, including population size fluctuations, family size variance, sex ratio, and taxonomic group. Comprehensive estimates, which included these factors, averaged 0.10–0.11, much lower than previously thought. This indicates that wildlife populations have smaller effective sizes than previously recognized. The study found that demographic and genetic methods yielded similar results when relevant variables were included. Life history characteristics and taxonomic groups had limited effects on Ne/N. Comprehensive estimates were significantly lower than previously assumed values, highlighting the need for careful consideration of N in conservation and management practices. The results emphasize the importance of accurate Ne/N estimates for assessing genetic health and viability in wildlife populations.The effective population size (Ne) is crucial for predicting inbreeding and genetic variation loss in wildlife. Since only census population size (N) is typically available, the ratio Ne/N is essential for evolutionary genetics and wildlife management. A review of 192 estimates from 102 species identified key variables affecting Ne/N, including population size fluctuations, family size variance, sex ratio, and taxonomic group. Comprehensive estimates, which included these factors, averaged 0.10–0.11, much lower than previously thought. This indicates that wildlife populations have smaller effective sizes than previously recognized. The study found that demographic and genetic methods yielded similar results when relevant variables were included. Life history characteristics and taxonomic groups had limited effects on Ne/N. Comprehensive estimates were significantly lower than previously assumed values, highlighting the need for careful consideration of N in conservation and management practices. The results emphasize the importance of accurate Ne/N estimates for assessing genetic health and viability in wildlife populations.