Abstract An experimental study was conducted to evaluate the buckling behavior of 190 Guadua bamboo culms of various lengths. These were subjected to an axial compressive load until failure. The geometrical and physical properties of each culm were measured, as well as its compressive strength and load carrying capacity. The buckling reduction factor (ψ) – which is the ratio of the ultimate buckling load (Fcr) to the ultimate compressive load (Fu) or the ratio of the ultimate buckling stress (σcr) to the ultimate compressive stress (σu) – was determined for each specimen. Several formulas were investigated by means of linear and non-linear regression in order to find the best fit for ψ. Separate models for intermediate and long members, as well as models combining the whole range of the slenderness ratios (λ) were proposed. Rankine-Gordon’s and Ylinen’s buckling formulas proved to be suitable to determine the buckling reduction factor for the whole range of slenderness ratios for the Guadua bamboo specimens studied, whilst Euler’s formula is more appropriate for longer columns. For the intermediate columns, the Newlin-Gahagan’s buckling formula was initially evaluated; however it was deemed unsuitable due to its unsatisfactory statistical performance. As a replacement, the Johnson buckling formula was derived. Ylinen’s buckling formula appears to provide the best fit and it is therefore recommended for Guadua column design. A maximum slenderness ratio was calculated at the ψ = 0.057, which resulted in a slenderness ratios of 139, 214, and 161, when calculated by Rankine-Gordon’s, Ylinen’s, and Euler’s buckling formula, respectively. Those ratios are approximately equivalent to 43, 67, and 50 length to diameter ratios (L/D). Since Ylinen’s equation is the best fit buckling formula among others, it is recommended that the length does not exceed 67 times the diameter (L/D