An image forming apparatus includes a second conveyance guide diverging from a first conveyance guide at a bifurcation and joining the first conveyance guide at a junction, the bifurcation being downstream of a first position of an image former in a conveyance direction, the junction being upstream of the first position in the conveyance direction, first and second sensors disposed in second and third positions between the junction and the first position along the first conveyance guide, respectively, and a controller that, when a sheet passes through the second and third positions for a second time, detects a surface characteristic of a side of the sheet by the first sensor and determines an image forming condition for the side based on the surface characteristic of the side and a basis weight detected by the second sensor when the sheet passed through the second and third positions for a first time.