Web tension in web material passing through a web transport system is determined in real time using position sensors coupled to driven rollers that define a beginning and an end of a tension zone. The position sensors on the rollers provide information related to the amount of strained web material that has been added and subtracted from the web material present in the tension zone. The amount of web material added to, subtracted from and present in the tension zone in a sample time period is then converted to an unstrained amount of web material that when combined provides an estimate for the present amount of unstrained web material present in the tension zone. Because the length of the tension zone is both fixed and known, the tension in the web material is determined from the present amount of unstrained web material in the tension zone.