Figure 3

Sources of error in knee-height measurement include incorrect leg position, incorrect placement of caliper, incorrect alignment of caliper to leg, and incorrect reading and rounding of the measurement.

The ability to predict standing height from knee-height measures is dependent on patient sex, age, and race. Persons of Hispanic and Asian descent are calculated using equations for White persons. Knee-height measures are entered into the following equations to estimate standing height.

Table 1. Calculations to Estimate Height from Knee Height According to Sex and Race

Sex	Age	Race	Calculation of Stature
Male	18-59	White	(KH x 1.88) + 71.85
	18-59	Black	(KH x 1.79) + 73.42
	60-80	White	(KH x 2.08) + 59.01
	60-80	Black	(KH x 1.37) + 95.79
Female	18-59	White	(KH x 1.86) – (age x 0.05) + 70.25
	18-59	Black	(KH x 1.86) – (age x 0.06) + 68.1
	60-80	White	(KH x 1.91) – (age x 0.17) + 75.0
	60-80	Black	(KH x 1.96) – (age x 1.96) + 58.72

KH = knee-height in centimeters; age = age in years

Because arm length tends to be proportional to height, arm span can be used to closely estimate height. Though arm span may not be as accurate as a good standing height, it can provide the clinician with a reasonable estimate of patient height. Arm span may be difficult to use in patients who experience contractures or other problems that prevent accurate measures.

To conduct an arm span measure, a straight measuring tape can be stretched across a floor or other large flat surface (see Figure 4). The patient should lie face down stretching arms perpendicular to the body at shoulder height across the tape. Measures should be recorded within .25 inch or 0.5 centimeter.

Alternately, a patient may be asked to hold one end of a tape measure with their middle finger at shoulder height. As the clinician holds the other end against the wall, the patient can then stand with their back to the wall while stretching arms out at shoulder height perpendicular to the body and parallel to the floor. Measure to the closest .25 inch or 0.5 centimeter.

Figure 4. Illustration of Arm Span Measurement

At this point you're probably wondering how measure