Optical calorimetry is a powerful technique for the characterization of porous materials within only a few minutes (e.g. specific surface area, adsorption capacity). In the current work, optical calorimetry is presented to be a versatile tool for the pore size characterization of activated carbons. Therefore, measurements were performed with six different test gases (N₂O, C₂H₆, C₃H₈, n-C₄H₁₀, i-C₄H₁₀, SF₆) in the optical calorimeter InfraSORP at ambient conditions. By combining the results of optical calorimetric measurement for each adsorptive, a pore size distribution (PSD) can be estimated in the range of 0.4–6 nm which is in accurate accordance with the PSD of reference CO₂ (273 K) and N₂ (77 K) physisorption experiments. While common physisorption experiments can easily take a few days, the PSD by using the optical calorimetric screening is obtained within roughly 1 h.