Image forming apparatus and image forming system capable of calculating actual development current using blank portion current and measuring development current

An image forming apparatus includes: a developing roller; a photosensitive drum; a first measurement device that measures a blank portion current in a first line on the photosensitive drum which extends in a scanning direction of the photosensitive drum and on which no toner patch is formed; a second measurement device that measures a measuring development current in a second line on the photosensitive drum which extends in the scanning direction of the photosensitive drum and on which a toner patch is formed; and a control device that functions as a patch setter and a first calculator. The patch setter sets a patch width of the toner patch in the scanning direction of the photosensitive drum. The first calculator calculates an actual development current based on a developable width of the photosensitive drum in the scanning direction, the patch width, the blank portion current, and the measuring development current.