BMI is a useful population screening tool but an imperfect individual measure. It doesn't distinguish muscle from fat, so very muscular people can read as 'overweight,' and it doesn't capture fat distribution. Combine it with waist measurement and body fat percentage for a fuller picture.

BMI Calculator

Q: How is BMI calculated?

BMI is weight in kilograms divided by height in metres squared: BMI = kg ÷ m². In imperial units it is 703 × pounds ÷ inches². Someone 5'9" (175 cm) weighing 160 lb (73 kg) has a BMI of about 23.6.

Q: What is a healthy BMI?

For adults the WHO classifies 18.5–24.9 as a healthy weight, under 18.5 as underweight, 25–29.9 as overweight, and 30 or above as obese. These ranges apply to adults over 20; children use age- and sex-specific percentiles.

Calculate your body mass index in metric or imperial units, see your WHO weight category, and find the weight range considered healthy for your height.

Your BMI

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How BMI is calculated

Metric: BMI = weight(kg) ÷ height(m)²
Imperial: BMI = 703 × weight(lb) ÷ height(in)²

Worked example

175 cm, 73 kg: 73 ÷ (1.75)² = 73 ÷ 3.0625 = BMI 23.8 — within the healthy range.

BMI categories (adults, WHO)

BMI	Category
Below 18.5	Underweight
18.5 – 24.9	Healthy weight
25.0 – 29.9	Overweight
30.0 and above	Obese

What BMI does and doesn't tell you

BMI is a fast, free screening number that correlates with health risk across populations — but for an individual it has real blind spots. It can't tell muscle from fat, so athletes often read "overweight" while carrying very little fat, and it says nothing about where fat sits (visceral belly fat is the riskier kind). Treat BMI as one input, not a verdict. For a fuller picture, add the body fat calculator and consider waist circumference. To act on the number, the calorie calculator and TDEE calculator translate a weight goal into daily targets. Read our explainer: What does my BMI actually mean?

Frequently asked questions

How is BMI calculated?

Weight(kg) ÷ height(m)², or 703 × lb ÷ in². 175 cm / 73 kg ≈ 23.8.

What is a healthy BMI?

18.5–24.9 for adults. Under 18.5 underweight, 25–29.9 overweight, 30+ obese.

Is BMI accurate?

Good for populations, imperfect for individuals — it ignores muscle mass and fat distribution.

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Medical disclaimer: BMI is a general screening estimate for adults over 20, not a diagnosis or medical advice. It does not apply to children, pregnant people, or athletes without additional context. Consult a healthcare provider about your individual health. Categories: World Health Organization. Last reviewed: July 2026.