How to know if your growth plates have closed?

The standard: test is a hand/wrist xray. "Bone age"(the status of the growth plates relative to sex and age-matched averages) is determined by comparing the xray to published standards.

X-rays can tell.: X-ray images of various long bones can give a pretty good indication, although not an exact time, as to where the growth plates are in closing.

Hand and Wrist Xray: For bone age. the classic atlas is by Gruelich and Pyle, but there are several online atlases as well. While the hand growth plates correlate with skeletal growth and all may be closed, there is still linear height growth in the spine even after all the long bones stop growing and with so many vertebral bodies, a 3/4 mm growth in each ( of 33) could still yield about inch in height on average

An x-ray: Of the end of your long bones, usually it is an x-ray of the left wrist joint, do determine bone age and whether growth plates have closed, best wishes