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Arm Muscle Area (AMA) Calculator

A nutrition-screening classic: strip the fat and bone out of your arm circumference to see the muscle.

How it is calculated

The tool treats the arm as a circle. Arm muscle circumference: AMC = MUAC − π × TSF, where MUAC is the mid-upper-arm circumference in cm and TSF is the triceps skinfold converted from mm to cm (÷ 10). Arm muscle area: AMA = AMC² ÷ (4π), in cm². The headline figure is the bone-corrected area, CAMA = AMA − 10 for men or AMA − 6.5 for women, which removes an estimated bone cross-section and never goes below zero. The result lists CAMA first, then AMA and AMC. If the skinfold is so large that AMC reaches zero or below, there is no result. The tool does not compare your value with reference percentiles.

Worked example

A man has a mid-upper-arm circumference of 30 cm and a triceps skinfold of 12 mm. Fat ring = π × 1.2 = 3.77 cm, so AMC = 30 − 3.77 = 26.23 cm. AMA = 26.23² ÷ (4π) = 54.75 cm². Subtracting the male bone correction of 10 gives a corrected arm muscle area of 44.75 cm². A woman with the same two measurements would get 54.75 − 6.5 = 48.25 cm², because her correction is smaller.

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Common mistakes

  • Entering the triceps skinfold in centimetres: the field is in millimetres, and a 12 mm fold typed as 1.2 removes almost no fat from the arm.
  • Using the largest bulge of the upper arm instead of the midpoint between the shoulder tip and the elbow for MUAC, and measuring with a tight or sagging tape.
  • Choosing the wrong sex, since the bone correction is 10 cm² for men and 6.5 cm² for women.
  • Reading a loose pinch as the true fold: a skinfold taken without lifting the fat cleanly from the muscle changes the result.
  • Comparing the corrected figure with published tables that use the uncorrected AMA, or the reverse; the two values differ by the bone correction.

Sources

About this calculator

Arm Muscle Area (AMA) is a nutrition-screening measurement calculated from just two numbers — mid-upper arm circumference (MUAC) and triceps skinfold thickness — using the formula AMA = [(MUAC − π × triceps skinfold)²] / (4π), which mathematically strips the subcutaneous fat ring off the arm to isolate the muscle-plus-bone cross-section. A “corrected” version subtracts a further estimate for bone area to isolate muscle alone, and converting that back into a circumference gives Arm Muscle Circumference.

Clinicians and dietitians use AMA as a quick bedside proxy for lean tissue and nutritional status when a DEXA scan or MRI isn't available — a low or declining AMA in a hospitalized or elderly patient is a red flag for malnutrition or muscle wasting (sarcopenia), since it can be tracked over time with nothing more than a measuring tape and skinfold calipers.

Measure the mid-upper arm circumference and the triceps skinfold to get arm muscle area, the bone-corrected arm muscle area and arm muscle circumference.

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