Aims and background: Modified Harvard step test (mHST) checks the aerobic fitness of an individual with a fixed step height of the stepper, which can be an advantage for taller people to perform mHST. Biomechanical characteristics change with each individual. Hence, by simply modifying the step height, the test can be individualized. Therefore, the aim of the study is to check whether an individualized change in the height of the stepper according to the hip joint angle affects the cardiorespiratory fitness index. Materials and methods: This is a comparative type of study conducted on 70 healthy young adults. Participants performed mHST using a stepper of height of 40 cm for males and 33 cm for females and an adjustable step test using a stepper with individualized calculated step height with a fixed hip angle of 70°. Outcome measures were physical fitness index (PFI) and maximal oxygen uptake (VO₂ max). Results: This study shows that there is a significant difference between the adjustable step test and mHST for PFI (p = 0.000) and VO₂ max (p = 0.000). The effect size of the adjustable step test for PFI and VO₂ max was large (r = 0.705; r = 0.629, respectively). Conclusion: Our study concludes that the height-adjustable step test estimates better PFI and shows better oxygen consumption or better VO₂ max. Clinical significance: Height adjustable step test estimates better PFI and shows better oxygen consumption or better VO₂ max.