This study examined the spatial variability of throughfall (T_f) and its implications for sampling throughfall during the leafless period of oak trees. To do this, we measured T_f under five single Brant’s oak trees (Quercus brantii var. Persica), in the Zagros region of Iran, spanning a six-month-long study period. Overall, the T_f amounted to 85.7% of gross rainfall. The spatial coefficient of variation (CV) for rainstorm total T_f volumes was 25%, on average, and it decreased as the magnitude of rainfall increased. During the leafless period, T_f was spatially autocorrelated over distances of 1 to 3.5 m, indicating the benefits of sampling with relatively elongated troughs. Our findings highlight the great variability of T_f under the canopies of Brant’s oaks during their leafless period. We may also conclude that the 29 T_f collectors used in the present study were sufficient to robustly estimate tree-scale T_f values within a 10% error of the mean at the 95% confidence level. Given that a ±10% uncertainty in T_f is associated with a ±100% uncertainty in interception loss, this underscores the challenges in its measurement at the individual tree level in the leafless season. These results are valuable for determining the number and placement of T_f collectors, and their expected level of confidence, when measuring tree-level T_f of scattered oak trees and those in forest stands.