An image forming apparatus includes a reading unit, a document conveyance unit, a sheet storage unit, a printing unit, a first and second determination unit, and a control unit. The reading unit reads a document. The printing unit performs printing on a sheet fed from the sheet storage unit. The first determination unit determines a first size of the document based on a size of a sheet stored in the sheet storage unit. The control unit causes the document conveyance unit to convey the document and causes the reading unit to read the document based on the determined first size. The second determination unit determines a second size of the conveyed document. In response to the determined first size not matching the determined second size, the control unit causes the document to be conveyed again and causes the document to be read again based on the determined second size.