Cardiorespiratory fitness (CRF) is an important indicator of adolescent cardiovascular well-being and future cardiometabolic health but not always feasible to measure. The purpose of this study was to estimate the concurrent validity of the non-exercise test (NET) for adolescents against the Progressive Aerobic Capacity Endurance Run (PACER®) and direct measures of VO2max as well as to examine the concurrent validity of the PACER® with a portable metabolic system (K4b2™). Forty-six adolescents (12–17 years) completed the NET prior to performing the PACER® while wearing the K4b2™. The obtained VO2max values were compared using linear regression, intra-class correlation (ICC), and Bland–Altman plots, and α was set at 0.05. The VO2max acquired directly from the K4b2™ was significantly correlated to the VO2max indirectly estimated from the NET (r = 0.73, p < 0.001, r2 = 0.53, ICC = 0.67). PACER® results were significantly related to the VO2max estimates from the NET (r = 0.81, p < 0.001, r2 = 0.65, ICC = 0.72). Direct measures from the K4b2™ were significantly correlated to the VO2max estimates from the PACER® (r = 0.87, p < 0.001, r2 = 0.75, ICC = 0.93). The NET is a valid measure of CRF in adolescents and can be used when an exercise test is not feasible.