The L-shell ionisation and X-ray production cross-sections of some post-transition elements: In, Sn and Tl, induced by protons of energies 1 MeV–4 MeV, have been calculated. The targets considered have few experimental cross-sections, for indium and tin, while thallium has no existing cross-section values in the database due to its radioactive and toxic nature. The cross-sections for the targets were obtained using computer codes based on the ECPSSR and SCA theories; and were subsequently validated using lead and bismuth targets whose experimental values are known within this energy range. The comparison of the experimental and calculated cross-sections showed that both models are in good agreement within certain proton energy region. However, above 2 MeV, the ECPSSR models should be employed. For the case where the SCA model is to be employed, the energy loss and Coulomb deflection factors should be taken into account.