An image forming apparatus includes an image forming unit forming an image on a first recording medium based on image data, a measurement unit being positioned in an immediate vicinity of the image forming unit, being arranged upstream of a sheet-conveyance path than the image forming unit, and measuring a size of the first recording medium, an expansion ratio calculation unit calculating an expansion ratio of the first recording medium based on a first size of the first recording medium obtained before the first recording medium is passed through the image forming unit and a second size of the first recording medium obtained after the first recording medium is passed through the image forming unit, and a correction unit correcting the image data used for forming another image on a second recording medium conveyed after the first recording medium based on the expansion ratio.