This disclosure relates to calibrating a volumetric estimation device for determining dimensions of an object. Two laser sources project two laser lines onto the object to form a rectangular calibration target. A camera captures an image of the rectangular calibration target and has a camera image plane and a camera image plane centre point. A processor measures the camera distortion effects to generate a filter to remove the distortion effects to approximate a pinhole camera. The camera image plane centre point and the points of projection of the laser sources are not collinear. The point of laser projection are not collinear with the camera image plane centre point. The processor uses locations of laser projected crosslines to determine a deviation angle from a direction perpendicular to the camera image plane and the distance between the camera image plane centre point and each laser source.