In the last decade, the rapid advancements in computational power have favored the development of high-resolution numerical models capable of directly resolving small-scale structures such as fronts and filaments. Such models have greatly improved our understanding of submesoscale dynamics. At the same time, the small dimensions and short duration of these structures still pose major challenges for small-scale dedicated field experiments. For this reason, submesoscale studies from in situ observations are still relatively scarce and quantitative estimates of key physical parameters for high-resolution numerical models, such as horizontal eddy diffusivity, are still lacking. This study presents a novel approach for computing in situ horizontal eddy diffusivity associated with frontal structures by combining cross-front widths derived from surface thermosalinograph sections with stirring rates estimated from Lagrangian drifter trajectories. The method is applied to the measurements collected across a frontal structure observed in the western part of the Gulf of Lion during the Latex10 campaign (LAgrangian Transport EXperiment, 1-24 September 2010). A total of 76 estimates of eddy diffusivity were obtained for strain rates of 0.70 and 1.21 day⁻¹ and front widths (horizontal scales) ranging between 1 and 4 km. The estimates are log-normally distributed, with 70% of the values ranging between 0.4 and 5 m² s⁻¹. Further analysis based on high-resolution simulations and remote sensed observations, as well as dedicated field experiments will help to assess the robustness of some of the assumptions at the base of the proposed approach, and to extend the results to different ocean regions.