A measurement method of nozzle overlapping width, in a main scanning direction intersecting a transport direction of a recording medium (P), in an ink jet recording apparatus including an image forming device , including a first head having a plurality of first nozzles aligned in a straight row, and a second head having a plurality of second nozzles aligned in a straight row, the image forming device being configured to eject ink on the recording medium (P) thereby forming an image, and a controller that controls the image forming device , the plurality of first nozzles in the first head being aligned along the main scanning direction, the plurality of second nozzles in the second head being aligned in a same direction in which the plurality of first nozzles are aligned, the first head and the second head being arranged such that a part of the plurality of first nozzles and a part of the plurality of second nozzles are located adjacent to each other, with a spacing in the transport direction, characterized in the measurement method comprising: a first step including causing the image forming device to form an image for measurement on the recording medium (P), using image data including combination patterns of droplet sizes, different with respect to each of blocks extending along the main scanning direction; a second step including causing the controller to select the block having uniform density along the main scanning direction, in the image for measurement; and a third step including causing the controller to determine the nozzle overlapping width using a droplet size ratio adopted to form the image for measurement, on a basis of a position of the selected block. the plurality of first nozzles in the first head being aligned along the main scanning direction, the plurality of second nozzles in the second head being aligned in a same direction in which the plurality of first nozzles are aligned, the first head and the second head being arranged such that a part of the plurality of first nozzles and a part of the plurality of second nozzles are located adjacent to each other, with a spacing in the transport direction, characterized in the measurement method comprising: a first step including causing the image forming device to form an image for measurement on the recording medium (P), using image data including combination patterns of droplet sizes, different with respect to each of blocks extending along the main scanning direction; a second step including causing the controller to select the block having uniform density along the main scanning direction, in the image for measurement; and a third step including causing the controller to determine the nozzle overlapping width using a droplet size ratio adopted to form the image for measurement, on a basis of a position of the selected block. a first step including causing the image forming device to form an image for measurement on the recording medium (P), using image data including combination patterns of droplet sizes, different with respect to each of blocks extending along the main scanning direction; a second step including causing the controller to select the block having uniform density along the main scanning direction, in the image for measurement; and a third step including causing the controller to determine the nozzle overlapping width using a droplet size ratio adopted to form the image for measurement, on a basis of a position of the selected block. <EOS>