Evaluating the variability between 20-m multistage fitness test estimating equations in law enforcement recruits. J Strength Cond Res XX(X): 000-000, 2022-The 20-m multistage fitness test (20MSFT) is commonly used by law enforcement agencies to measure aerobic fitness and to estimate maximal aerobic consumption (V̇o2max). These measures are an important occupational variable with aerobic fitness levels linked to employment status, occupational performance, and long-term health in law enforcement officers. There are a multitude of predictive equations used to provide an estimate of V̇o2max, with the extent of variability in the estimated V̇o2max currently unknown in this population. This has consequences for comparisons between, and across, differing agencies, and in capabilities of deriving normative data. The aim of this investigation was to compare the variability in estimated V̇o2max scores derived from different 20MSFT predictive equations. The 20-m multistage fitness test data from 1,094 law enforcement recruits (male n = 741, 25.2 ± 6.3 years; female: n = 353, 25.6 ± 5.6 years) from a single agency were retrospectively analyzed. The 20MSFT scores were transformed into estimated V̇o2max scores using 6 different predictive equations. Significance was set at p < 0.05. Results demonstrated significantly different V̇o2max scores between each predictive equation (p < 0.001; d = 0.25-1.53) and between male and female recruits (p < 0.001, r = 0.55). All estimated V̇o2max equations showed small to very strong correlations with each other (p < 0.001; r = 0.32-0.99). The findings indicate considerable dispersion of V̇o2max scores when using differing equations, suggesting raw 20MSFT variables (e.g., shuttles or distance completed) should be preferred to measure and apply results from aerobic fitness tests if standardized approaches are not developed within law enforcement.