A new clinically accessible measure of balance, functional reach (FR), is the difference between arm's length and maximal forward reach, using a fixed base of support. The purposes of this study were to (a) establish FR as a measure of the margin of stability versus the laboratory measure, center of pressure excursion (COPE); (b) test reliability and precision, and (c) determine factors that influence FR, including age and anthropometrics. We evaluated FR in 128 volunteers (age 21-87 years). FR was determined with a precise electronic device and a simple clinical apparatus (yardstick). FR correlates with COPE (Pearson r = .71) and is precise (coefficient of variation = 2.5%) and stable (intraclass correlation coefficient across days = .81). Age and height influence FR. FR is portable, inexpensive, reliable, precise, and a reasonable clinical approximator of the margin of stability. FR may be useful for detecting balance impairment, change in balance performance over time, and in the design of modified environments for impaired older persons.