The invention relates to a method for estimating a dose administered by a radiology system provided with an X-ray source and a flat surface sensor, wherein (a) an X-ray image of the patient is acquired by the flat surface sensor; (b) the grey level of the pixel is determined at the centre of the X-ray image; (c) the kerma K is calculated, on the patient's entrance from the grey level, from the electrical charge passing through the X-ray tube during the patient's exposure time, the thickness of the patient's body along the axis of the X-ray beam and the distance between the X-ray source and the patient. This method of estimating dose can significantly reduce the margin of error on the dose administered.