Arm Muscle Area Calculator (Mid-Upper Arm Muscle Circumference and Area)
Calculate mid-upper arm muscle circumference, arm muscle area (corrected for bone, Heymsfield), arm fat area and arm fat index from arm circumference and triceps skinfold.
How it works
AMC (cm) = MUAC − π × TSF (cm) · AMA = AMC² ÷ 4π · corrected AMA = AMA − 10 (men) or − 6.5 (women) · total arm area = MUAC² ÷ 4π · arm fat area = total − AMA · arm fat index = arm fat area ÷ total area × 100
Mid-upper arm anthropometry is a quick bedside way to estimate muscle and fat reserves when weighing is difficult. Treating the arm as a cylinder, subtracting the skinfold ring from the circumference gives the arm muscle circumference, and from it the cross-sectional muscle area. Heymsfield et al. (1982) showed that subtracting 10 cm² in men and 6.5 cm² in women removes the humerus and makes the result track total muscle mass better. Results are usually compared with Frisancho’s age- and sex-specific percentile tables.
Worked example
A man with a 30 cm arm circumference and a 12 mm triceps skinfold: AMC = 30 − π × 1.2 = 26.2 cm; AMA = 26.23² ÷ 12.566 = 54.8 cm²; corrected AMA = 54.8 − 10 = 44.8 cm². Total arm area = 71.6 cm², arm fat area = 16.9 cm² and arm fat index 23.6%.
Sources: Heymsfield SB et al. (1982) Anthropometric measurement of muscle mass: revised equations for calculating bone-free arm muscle area. Am J Clin Nutr 36:680–690 · Frisancho AR (1981) New norms of upper limb fat and muscle areas for assessment of nutritional status. Am J Clin Nutr 34:2540–2545
Frequently asked questions
How do I measure mid-upper arm circumference?
With the arm bent at 90°, find the midpoint between the acromion (shoulder tip) and the olecranon (elbow). Let the arm hang relaxed and wrap a non-stretch tape around it at that mark, snug but not compressing the skin.
Where is the triceps skinfold taken?
At the same midpoint on the back of the arm, over the triceps, with the arm relaxed. Pinch a vertical fold, apply the calliper 1 cm below the fingers and read after about 2 seconds; take the average of two or three readings.
What is a low arm muscle area?
It depends on age and sex. Clinicians usually compare corrected AMA with Frisancho’s percentiles: below the 5th percentile suggests depleted muscle reserves, and the 5th–15th percentile a moderate deficit.
Why correct for bone?
The uncorrected area includes the humerus, which does not change with nutrition. Removing a fixed bone area makes changes in the result reflect muscle alone, especially in people with low muscle mass.
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This calculator is an educational aid for nutrition and health professionals. It does not replace a clinical assessment — measurement technique strongly affects the result, so interpret it with a qualified professional.