Ulna Length as a Surrogate Measure Ulna length is a measurement of the forearm bone, used to estimate a person's full height when a direct standing measurement is impossible (e.g., in bedridden, elderly, or disabled patients). Purpose: Its primary use is to calculate Body Mass Index (BMI) for nutritional screening. How it Works: The measured length is entered into a simple, population-specific formula to predict full height. Key Feature: It is a quick and practical alternative to knee height, of