Why estimate height this way
Standing height can’t always be measured directly — for example, for someone who uses a wheelchair or has a spinal curvature. In these cases, clinicians and nutrition screening tools estimate height from a forearm (ulna) length measurement instead, since limb length correlates closely with overall stature.
The formula used
This calculator uses regression equations from clinical nutrition screening research (the method behind tools such as the UK’s MUST screening tool), which differ by sex and by whether the person is under or at least 65 years old, since limb-to-height proportions shift slightly with age. The ulna is measured from the point of the elbow to the prominent wrist bone on the same arm.
Note: this is an estimate, not a precise measurement, and typical accuracy is within a few centimeters. It is intended for general and educational use, not as a substitute for a clinical assessment.