During the Calvin Cycle, the point at which G3P leaves the cycle and is converted to glucose is in the second phase of the cycle, known as the reduction phase.
In this second phase, PGA is reduced to G3P (glyceraldehyde 3 Phosphate using ATP and NADH. Some of the G3P at this point are shunted out of the cycle and are converted into glucose and other sugars.
Two molecules of G3P (the output of carbon fixation and reduction) are required to produce a single six-carbon molecule of glucose.
