An attempt was made to calculate the spur size in liquid water at room temperature from fundamental interactions. Electron trapping, elastic scattering, and positive-ion back attraction undergone in subexcitation and sub-vibrational stages in the 100 fs time scale for thermalization were considered and included in the model. Overall diffusional broadening was estimated to be 41.2 angstrom, attended by the positive-ion pull back of 24.0 angstrom, resulting in a calculated spur size of 17.2 angstrom. Electron trapping is seen in competition with thermalization in the ultimate stage, which results in the trapped electron position distribution as a sum of Gaussians. (C) 2016 Elsevier B. V. All rights reserved.