<p>Desiccation cracking significantly impacts the engineering properties of soils, influencing fluid infiltration and structural stability. A key phenomenon in desiccation cracking is the size effect, where soil dimensions, including thickness and radius, alter cracking behavior. However, the size effect remains poorly understood, particularly in linking laboratory-scale findings to field conditions. Existing studies are often limited to small laboratory samples, leading to discrepancies in crack behavior across scales and a lack of standardized guidelines for determining suitable sample sizes in laboratory tests. This study investigates the size effect on desiccation cracking in clayey soils and identifies suitable laboratory sample sizes to represent field-scale cracking patterns. Desiccation tests were performed on soil samples with varying radii (25–100&#xa0;mm) and thicknesses (5–18&#xa0;mm). Cracking behavior during drying and equilibrium-state crack patterns were analyzed. A size parameter (<i>λ</i>), defined as the ratio of sample radius to thickness, was introduced to characterize the soil's volumetric size. Results reveal three distinct stages of the size effect: (i) the crack-free stage (<i>λ</i> &lt; <i>λ</i>_c), with no visible cracks; (ii) the size-dependent stage (<i>λ</i>_c &lt; <i>λ</i> &lt; <i>λ</i>_t), where cracking behavior changes significantly; and (iii) the size-insensitive stage (<i>λ</i> &gt; <i>λ</i>_t), where crack parameters stabilize. Two critical size parameters, the critical cracking size (<i>λ</i>_c ≈4.0) and the transition size (<i>λ</i>_t ≈9.0), were identified. The proposed size thresholds (<i>λ</i>_c and <i>λ</i>_t) were found to be applicable across different clayey soils, suggesting the general relevance of the framework for scaling desiccation cracking behavior in diverse geotechnical contexts. These findings enhance the understanding of size effects and provide a framework for optimizing laboratory tests to better reflect field conditions.</p>