An image forming apparatus includes an image forming device; an imaging device; and at least one processor including a pattern forming unit to cause a recording head to form a pair of first marks, with first and second nozzles disposed at a first distance from each other in a direction of conveyance of a recording medium, while the recording head moves in a first direction and cause the recording head to form a second mark while the recording head moves in a second direction, a position detector to detect positions of the first and second marks in a captured image, a ratio calculator to calculate a ratio between a distance between the first marks in the captured image and a deviation of the second mark in the captured image, and distance calculator to calculate a distance of the deviation based on the first distance and the ratio.