A method for ultrasonic geometry testing of a rotationally symmetric test object at a plurality of different measuring positions (x n) distributed along a surface of a test object, by means of two ultrasonic transducers diametrically facing each other, the method involving the following steps: a step of providing a rotationally symmetric calibration device with known dimension (OD cal (x n)); several subsequent calibrating steps at measuring positions (x n) located on a circumference around the calibration device, during each of which a measuring position specific distance (WP i (x n)) between the calibration device and each ultrasonic transducer is determined and recorded by an ultrasonic transit time method, by means of at least one echo on at least one surface of the calibration device, using the measuring position specific distance (WPi(xn)) and the known dimension ((OD cal (x n)) to calculate a stretch of movement (Axn) between the ultrasonic transducers for each measuring position; (x n); subsequently a step of providing a test object; several test steps in the ultrasonic transit time measurement on the test object at measuring positions (x n) which correspond to those of the calibrating steps so that the stretch of movement (Axn) does not change, wherein at the plurality of measuring positions (x n) transit time measurements are taken by means of at least one echo on at least one surface of the test object, so as to determine a measuring position specific distance (WP' i (x n)) between the test object and each ultrasonic transducer; and at least one evaluation step, wherein, using the measuring position specific distances (WP' i (x n)) for the test object and the stretch of movement (Axn), an outer diameter (27, OD sample (x n)) of test object is calculated, in particular for each measuring position (x n) one dimension (27, OD sample (x n); wherein two phased arrays (30 1, 30 2) diametrically facing each other and each consisting of several ultrasonic transducers are used for the calibrating steps and the test steps; wherein intermediately or simultaneously with the testing and calibrating steps, a rotating relative movement is carried out between the ultrasonic transducers and calibration device or test object; wherein, in each calibrating step, and in each test step for each measuring position (x n) two distances (WP1(x n), WP2(x n), WP1'(x n),WP 2 '(x n)) of the pair of phased arrays (30 1, 30 2) are measured or determined; and wherein the ultrasound transducers of the phased array are selectively actuated and define different measuring positions (x n) which are equally valid for both calibration and test steps. a step of providing a rotationally symmetric calibration device with known dimension (OD cal (x n)); several subsequent calibrating steps at measuring positions (x n) located on a circumference around the calibration device, during each of which a measuring position specific distance (WP i (x n)) between the calibration device and each ultrasonic transducer is determined and recorded by an ultrasonic transit time method, by means of at least one echo on at least one surface of the calibration device, using the measuring position specific distance (WPi(xn)) and the known dimension ((OD cal (x n)) to calculate a stretch of movement (Axn) between the ultrasonic transducers for each measuring position; (x n); subsequently a step of providing a test object; several test steps in the ultrasonic transit time measurement on the test object at measuring positions (x n) which correspond to those of the calibrating steps so that the stretch of movement (Axn) does not change, wherein at the plurality of measuring positions (x n) transit time measurements are taken by means of at least one echo on at least one surface of the test object, so as to determine a measuring position specific distance (WP' i (x n)) between the test object and each ultrasonic transducer; and at least one evaluation step, wherein, using the measuring position specific distances (WP' i (x n)) for the test object and the stretch of movement (Axn), an outer diameter (27, OD sample (x n)) of test object is calculated, in particular for each measuring position (x n) one dimension (27, OD sample (x n); wherein two phased arrays (30 1, 30 2) diametrically facing each other and each consisting of several ultrasonic transducers are used for the calibrating steps and the test steps; wherein intermediately or simultaneously with the testing and calibrating steps, a rotating relative movement is carried out between the ultrasonic transducers and calibration device or test object; wherein, in each calibrating step, and in each test step for each measuring position (x n) two distances (WP1(x n), WP2(x n), WP1'(x n),WP 2 '(x n)) of the pair of phased arrays (30 1, 30 2) are measured or determined; and wherein the ultrasound transducers of the phased array are selectively actuated and define different measuring positions (x n) which are equally valid for both calibration and test steps.