This terms is best used for plant with more or less synchronous fruit development and can only be used of the final size of the fruit is known. This stage is to be used for the development stage of a whole plant (PO:0000003). For an individual fruit, use fruit size 30 to 50% stage (PO:0025506).

whole plant fruit formation stage 30 to 50%

A whole plant fruit formation stage (PO:0007042) that spans the interval when the average size of fruits (PO:0009001) on a whole plant (PO:0000003) has reached 30% to 50% of its final size.