Calculators

Anorexic BMI Calculator

Gender
in
lbs
25 years
Your BMI17.2
CategoryUnderweight
Health Risk LevelModerate

This educational tool maps a Body Mass Index value onto the low-end thresholds clinicians use when screening for severe underweight and possible eating disorders such as anorexia nervosa. It splits the usual "underweight" band into finer tiers and pairs each with a relative health-risk level so a dangerously low result stands out. It is an awareness aid, not a diagnosis: only a qualified professional can diagnose an eating disorder.

Formula

BMI = weight (kg) / height (m)²

weight
Body weight in kilograms (pounds × 0.453592)
height
Standing height in metres (inches × 2.54, then ÷ 100)
BMI
Body Mass Index in kg/m², the value scored against the underweight tiers

How it works

  1. Enter your height in inches and your weight in pounds; the tool converts them to metric internally (2.54 cm per inch, 0.453592 kg per pound) before computing BMI.
  2. BMI is computed as weight in kilograms divided by height in metres squared, exactly like a standard BMI.
  3. The result is placed in a low-range tier — Very Severely Underweight (BMI under 15), Severely Underweight (15 to under 16), Underweight (16 to under 18.5), Normal (18.5 to under 25), or Overweight or Above (25 and up) — and tagged with a health-risk level from Critical down to N/A.

Worked examples

A person 5 ft 7 in (67 in) tall weighing 95 lb checks where they fall on the underweight scale.

  1. Convert: height 67 × 2.54 = 170.18 cm = 1.7018 m; weight 95 × 0.453592 = 43.09 kg.
  2. BMI = 43.09 ÷ (1.7018 × 1.7018) = 43.09 ÷ 2.8961 = 14.88.
  3. A BMI below 15 falls in the lowest tier.

BMI ≈ 14.9 → Very Severely Underweight, Critical health risk.

A person 5 ft 5 in (65 in) tall weighing 100 lb wants their tier.

  1. Convert: 65 × 2.54 = 165.1 cm = 1.651 m; 100 × 0.453592 = 45.36 kg.
  2. BMI = 45.36 ÷ (1.651²) = 45.36 ÷ 2.7258 = 16.64.
  3. A BMI of 16 to under 18.5 sits in the Underweight tier.

BMI ≈ 16.6 → Underweight, Moderate health risk.

Frequently asked questions

Can this calculator diagnose anorexia?
No. Anorexia nervosa is a clinical diagnosis based on behaviour, psychology, and physical signs, not on a single number. A very low BMI can be one warning sign, but only a doctor or mental-health professional can diagnose an eating disorder.
Why split the underweight range into several tiers?
A standard BMI tool lumps everything below 18.5 into one "underweight" label. Splitting it at 15 and 16 highlights the severely and very-severely underweight zones, where medical risks like organ stress and electrolyte imbalance rise sharply.
What BMI is considered dangerously low?
This tool flags a BMI under 16 as Severely Underweight and under 15 as Very Severely Underweight with a Critical risk level. Persistent values in this range warrant prompt medical attention.
Where can I get help for an eating disorder?
If you or someone you know may have an eating disorder, contact a physician or a national eating-disorder helpline. Early professional support greatly improves recovery outcomes.

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