The paper proposes a model relating the level of reinforcement corrosion (in terms of loss of rebar radius) with the width of corrosion-induced cracks. The model is developed using a simulation of the process of corrosion-induced crack opening by means of finite-element (FE) modelling. Concrete is treated as a linear elastic material, a vertical crack is introduced above a reinforcing bar and expansive behaviour of corrosion products is modelled using a thermal analogy. Corrosion products are divided into those that penetrate (dissipate) into cracks (no crack propagation) and those that cause crack opening. The amount of corrosion products penetrating into cracks at a specified crack width is evaluated using FE modelling and analyses of experimental results. It was found that a corrosion loss of 0.1-0.4 mm dissipated into the cracks when the crack width was 1.0 mm. The influence of geometric parameters such as rebar diameter, spacing and location, and thickness of top and edge concrete covers were investigated. The limits of applicability of the proposed relationships were established using non-linear FE modelling.