A focal spot sensing device includes: a housing that resists x-ray beams; an opening disposed in a wall of the housing that allows an x-ray beam to enter the housing; and a sensor device disposed in the housing that interprets a position of the x-ray beam for calculating a position of a focal spot. An imaging system includes: an x-ray source that produces an x-ray beam and has a focal spot; a detector array that receives the x-ray beam and includes a focal spot sensing device, the focal spot sensing device includes: a housing that resists x-ray beams; an opening disposed in a wall of the housing that allows the x-ray beam to enter the housing; and a sensor device disposed in the housing that interprets a position of the x-ray beam for calculating a position of the focal spot. A method for sensing a focal spot, the method includes: receiving an x-ray beam into an opening of a focal spot sensing device; interpreting a position of the x-ray beam; and calculating or measuring a position of a focal spot.