A method for inspecting a wafer, includes: rotating the wafer about an axis of the wafer, emitting from a light source, two pairs of incident coherent light beams, each pair forming, at the intersection between the two beams, a measurement volume, a portion of the main wafer surface passing through each of the measurement volumes during the rotation, collecting a light beam scattered by the wafer surface, capturing the collected light and emitting an electrical signal representing the variation in the collected light intensity, detecting in the signal, a frequency, being the time signature of a defect through a respective measurement volume, for each detected signature, determining a visibility parameter, on the basis of the visibility determined, obtaining an item of information on the size of the defect, and cross-checking the items of information to determine the size of the defect.