A print media in a printing system includes multiple test patterns with each test pattern having one or more marks. Each test pattern can have a different number of marks. A method for detecting size variations in the print media while the print media is moving through the printing system includes scanning the test patterns as the print media is moving in a transport direction to produce test pattern signals, with each signal representing a respective test pattern, and analyzing the measured test pattern signals to determine whether a size variation has occurred in the print media. One or more compensation values can be determined based on the size variation. If a size variation is detected, the operation or setting of one or more components in the printing system can be adjusted based on the one or more compensation values.