A modular wheel-hub bearing unit having an outer flanged hub for mounting the unit on an upright of a vehicle, provided externally with an assembly surface and internally with a mounting seat; and a bearing provided with an outer ring, two inner rings and two rows of rolling elements arranged between the outer ring and the two inner rings. The bearing being mounted inside the assembly seat independently of the outer flanged hub and having an outer diameter, the dimensions of which are related to the dimensions of an outer diameter of the assembly surface of the flanged hub by a first coefficient (α) according to the relation: D2=α*D1, where 0.80≤α≤0.95.