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BMI calculator (with Asian cut-offs)

Body mass index with the lower cut-offs used for South Asian adults.

What this calculator is for

Body mass index is a quick screen for underweight and excess weight in adults. South Asians develop type 2 diabetes, hypertension and heart disease at lower BMIs than white Europeans, so this calculator uses the lower action points recommended for Asian populations by a WHO expert consultation and by NICE.

The formula

BMI = weight (kg) ÷ height (m)².

Cut-offs

  • Below 18.5: underweight.
  • 18.5–22.9: healthy range for South Asian adults.
  • 23–27.4: overweight (increased risk). The general WHO cut-off is 25.
  • 27.5 or more: obese (high risk). The general WHO cut-off is 30.

Worked example

A man weighing 68 kg and 170 cm tall: 68 ÷ (1.70 × 1.70) = 23.5 kg/m². By the general cut-offs he is "healthy", but by the South Asian action points he is overweight and should be checked for diabetes, blood pressure and lipids.

Using it in clinic

  • Combine BMI with waist measurement. NICE suggests a waist-to-height ratio of 0.5 or more indicates increased central fat; keep the waist under half the height.
  • A raised BMI is a prompt to screen with HbA1c or fasting glucose, blood pressure and a lipid profile, and to discuss diet and activity.
  • Record BMI at booking in pregnancy, before surgery and when starting drugs that cause weight gain.

Limitations and pitfalls

  • BMI does not separate muscle from fat. Muscular young men can read "obese" without excess fat.
  • It is not valid in pregnancy, in oedema or ascites, or in amputees.
  • Do not use adult cut-offs in children and adolescents: plot BMI on age- and sex-specific centile charts.
  • In older adults, a low BMI and unintentional weight loss often matter more than a high one.
  • Weigh and measure the patient; reported heights and weights are often wrong.

See the textbook chapters on nutrition and malnutrition and diabetes mellitus, medical OPD and atorvastatin.

Frequently asked questions

What is a normal BMI for Pakistanis?

For South Asian adults, 18.5–22.9 kg/m² is the healthy range. Overweight starts at 23 and obesity at 27.5, lower than the general cut-offs of 25 and 30.

Why are BMI cut-offs lower for South Asians?

South Asians carry more body fat and central fat at the same BMI and develop diabetes and heart disease at lower weights, so action points are set lower.

Can I use this BMI calculator for children?

No. Children and adolescents need BMI plotted on age- and sex-specific centile charts.

Is waist size better than BMI?

They answer different questions. Waist size shows central fat, which links closely with diabetes and heart disease. Use both; a waist under half your height is a simple target.

A calculator supports, but does not replace, clinical judgement. Check results before acting on them.