<p>An extensive experimental and numerical analysis was conducted to examine the axial compressive behavior of circular concrete-filled steel tube (CFST) columns. A total of 24 specimens with varying geometrical and material parametersincluding three heights (<i>L</i>), three diameters (<i>D</i>), two wall thicknesses (<i>t</i>), and two concrete strength (<i>f</i>_<i>c</i>) classes were tested to assess the effects of slenderness (<i>L</i>/<i>D</i>), sectional slenderness (<i>D</i>/<i>t</i>), and strength index (<i>SI</i>) on the ultimate load capacity of CFST columns. The experimental results indicated that increasing concrete strength enhances the ultimate load capacity, whereas higher <i>L</i>/<i>D</i> ratios lead to pronounced strength reduction. Finite element (FE) models developed in ANSYS were validated against the test data and exhibited excellent agreement, with FE predictions slightly exceeding experimental values. The axial capacities were also evaluated according to AISC 360-16 and Eurocode-4 provisions, with Eurocode-4 yielding closer predictions to the experimental findings. In addition, Strength Index-Slenderness (<i>SI-L</i>/<i>D</i>) plots have been created to estimate the ultimate load-carrying capacities of CFST columns. A practical approach has been proposed using these plots. This approach has demonstrated a robust correlation with the design standards for the evaluation of CFST columns.</p>