Recycling of CO2 emissions by direct electrocatalytic reduction of CO2 has been pointed out as a feasible method for CO2 conversion into useful chemical products and fuels. In particular, formic acid (HCOOH) represents one of the most interesting products obtained, since HCOOH is widely used in different industrial applications, as well as, it has been proposed as a renewable hydrogen carrier and suitable fuel for fuel cells [1]. Among the group of metals with high hydrogen evolution reaction overpotential and high selectivity towards HCOOH production, Sn exhibits the lowest toxicity and represents one of the best options in terms of cost and selectivity [2]. Electroreduction of CO2 on spherical Cu nanoparticles has been recently proved as a surfacesensitive reaction [3], where the product selectivity is drastically affected by the particle size. Nevertheless, no attention has been paid to evaluate the electrochemically active area in Sn supported electrodes, which does not allow the proper evaluation of the particle size effect in the electrocatalytic reduction of CO2 on Sn particles. This is because there is not an specific chemisorption reaction to measure the catalytic surface of Sn electrodes. For this reason, we propose N2 physisorption, which is a non‐selective method for Sn, but can be applied to measure non supported Sn nanoparticles surface area by assuming negligible surface lost after being deposited on the support. This approach for evaluating Sn particles surface area allow us to present experimental evidences of no significant particle size effects in the electrocatalytic reduction of CO2 on Sn nanoparticles, neither in activity nor in reaction selectivity down to 15 nm size. References [1] D. Du, R. Lan, J. Humphreys, S. Tao, J. Appl. Electrochem. 47 (2017) 661. [2] A. Del Castillo, M. Alvarez‐Guerra, J. Solla‐Gullón, A. Sáez, V. Montiel, A. Irabien, J CO2 Util. 18