The study aimed to identify a small set of fitness tests that could effectively predict performance in simulated firefighting tasks. Thirty-six (25 male and 11 female) firefighters participated in the study. Strength was evaluated with grip strength, barbell bench rows, and elevated trap bar deadlifts. Work capacity was assessed using a 3-minute pyramid test, executed with and without firefighting equipment. Firefighting performance was evaluated using a simulated work task course comprising stair climbing, hose pull, victim rescue, and equipment carry. We used backward linear regressions to derive models incorporating fitness test results, demographic variables, and oxygen uptake measures as predictors. Statistical significance was set to p < 0.05. The pyramid test without equipment accounted for 59% of the variance in task performance. When body mass and height were included, the model's predictive power increased to 71%. A final model, integrating the pyramid test, body mass, and absolute maximal oxygen uptake capacity (V̇o2max), explained 81% of performance variation. Our findings indicate that V̇o2max is the key factor in firefighter task performance, explaining 69% of the variance. The pyramid test, which estimates V̇o2max and predicted 59% of performance, is simple, time efficient, and can be conducted at stations to assess physical ability and work capacity. Incorporating the pyramid test into regular assessments can help firefighters focus on improving their work capacity, which is essential for achieving better performance.