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BMI Calculator

Calculate your Body Mass Index from height and weight.

Measurements
ft in
lbs

How It Works

Body Mass Index (BMI) is calculated as weight in kilograms divided by height in meters squared (kg/m²). In imperial units the formula is (lbs ÷ inches²) × 703. The World Health Organization defines four adult categories:

  • Underweight — BMI below 18.5
  • Normal weight — BMI 18.5 to 24.9
  • Overweight — BMI 25 to 29.9
  • Obese — BMI 30 and above

Worked examples:

  • 5 ft 9 in (69 in), 160 lbs → BMI = (160 ÷ 69²) × 703 = (160 ÷ 4761) × 703 ≈ 23.6 — Normal weight.
  • 175 cm, 90 kg → BMI = 90 ÷ 1.75² = 90 ÷ 3.0625 ≈ 29.4 — Overweight.

BMI is a useful population-level screening tool but has well-known limitations: it doesn't distinguish muscle from fat, varies by age and ethnicity, and can misclassify muscular athletes as overweight. Always consult a healthcare provider for a full health assessment.

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Frequently Asked Questions

What is a healthy BMI for adults?

The WHO considers a BMI of 18.5 to 24.9 to be a healthy (normal) weight for adults. Below 18.5 is underweight, 25–29.9 is overweight, and 30 or above is classified as obese.

How is BMI calculated?

BMI = weight (kg) ÷ height (m)². In imperial units: BMI = (weight in pounds ÷ height in inches²) × 703. For example, a person who is 5 ft 6 in (66 inches) and 150 lbs has a BMI of (150 ÷ 4356) × 703 ≈ 24.2.

Is BMI accurate for everyone?

BMI is a screening tool, not a diagnostic measure. It does not account for muscle mass, bone density, age, sex, or ethnicity. Athletes may be classified as overweight despite having low body fat. For a complete picture, consult a healthcare provider.

What BMI is considered obese?

A BMI of 30 or higher is classified as obese by the WHO. This is further divided into Class I (30–34.9), Class II (35–39.9), and Class III (40 and above), sometimes called severe or morbid obesity.

How much do I need to weigh to reach a normal BMI?

Use the target weight ranges shown in the calculator's results table. For example, if you are 5 ft 8 in (68 in), a normal BMI (18.5–24.9) corresponds to roughly 122–164 lbs.