The invention provides an image forming system, which includes: an image forming unit that forms a first color patch on a paper medium and a second color patch having a position different from the first color patch and having the same color as the first color patch; a scanner that reads respective colors of the first color patch and the second color patch formed on the paper medium by the image forming unit; a colorimeter that performs colorimetry to the first color patch formed on the paper medium by the image forming unit; a detector that detects a temperature of the first color patch; and acorrection unit that corrects, based on a reading result of the scanner, a colorimetry result of the colorimeter, and a temperature of the first color patch detected by the detector, a reading resultof a third color patch different in position from the first color patch and the second color patch.