A bale measuring method for a rectangular baler having a bale chamber in which bales are formed. The bale measuring method includes steps of measuring a movement of crop material downstream of the bale chamber as the crop material moves backward in the baler, using the measured movement of the crop material downstream of the bale chamber to calibrate a measurement and calculation tool for measuring a movement of crop material in the bale chamber and for calculating a length of a bale being formed in the bale chamber based on the measurement, and determining the length of the bale being formed in the bale chamber using the calibrated measurement and calculation tool as the bale moves backward in the baler.