Upper to Lower Segment Ratio

The upper-to-lower body segment ratio is the length from the top of the symphysis pubis to the top of the head, divided by the length from the top of the symphysis pubis to the sole of the foot. In bony dysplasias such as achondroplasia or hypochondroplasia, the upper to lower segment ratio is abnormally high for the child’s age (ie, the upper segment is significantly longer than the lower segment).

The segments are calculated by:

1. Measuring from the symphysis pubis to the floor to measure the lower segment
2. Subtracting the lower segment from the total height or total length to give the upper segment
3. Dividing the length of the upper segment by the length of the lower segment

Following is a chart of upper-to-lower body segment ratios.