BMI Calculator
The BMI calculator uses your height and weight to calculate your Body Mass Index, a common screening tool used by healthcare professionals to assess weight status.
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Calculator
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Formula
BMI = Weight (kg) ÷ Height (m)²
Divide your weight in kilograms by your height in meters squared. If you use imperial units, divide weight in pounds by height in inches squared, then multiply by 703. The result is a dimensionless number that falls into standard WHO weight categories.
How to use the BMI Calculator
- 1
Enter your weight
Value should be in kg.
- 2
Enter your height
Value should be in cm.
- 3
Read your results instantly
Results update in real time as you type.
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BMI categories and what they mean
The World Health Organization defines four main BMI categories: Underweight (below 18.5), Normal weight (18.5–24.9), Overweight (25–29.9), and Obese (30 and above). Class III obesity (sometimes called severe obesity) begins at 40.
These categories were established based on population studies linking BMI ranges to health risk outcomes like cardiovascular disease, type 2 diabetes, and all-cause mortality.
The well-known limitations of BMI
BMI is a blunt instrument. It doesn't distinguish between muscle and fat — a muscular athlete can have a BMI in the 'overweight' range while carrying minimal body fat. It also doesn't account for fat distribution: abdominal fat is significantly more metabolically harmful than fat stored in the hips and thighs.
Age and sex matter too. Older adults naturally carry more fat at the same BMI, and women typically have higher body fat percentages than men at equal BMIs. Many clinicians now use BMI alongside waist circumference and body fat percentage for a fuller picture.
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BMI in children and adolescents
For adults 20+, fixed BMI ranges apply. For children and teens (2–19), BMI is interpreted differently — using age- and sex-specific percentile charts. A child at the 85th to 95th percentile is considered overweight; above the 95th percentile is obese.
This calculator is designed for adults. For pediatric BMI, use age-specific CDC growth charts.
What to do if your BMI is outside the normal range
A BMI above or below the normal range is a signal to look closer, not a diagnosis. Consult a healthcare provider who can assess the full picture: blood pressure, cholesterol, blood glucose, waist circumference, lifestyle factors, and family history.
Small changes can have outsized impact. Even a 5–10% reduction in body weight has been shown to significantly improve metabolic markers in overweight individuals.
Tips & Insights
Waist circumference adds important context
The CDC recommends waist circumference alongside BMI. Risk increases substantially for men with waist >40 inches (102cm) and women >35 inches (88cm), regardless of BMI category.
BMI and insurance
Some life insurance companies use BMI as a rating factor. A BMI in the normal range can qualify you for preferred rates. This is one practical financial reason to track it.
The Asian BMI adjustment
Many health organizations recommend lower BMI thresholds for people of Asian descent, as metabolic risk appears at lower BMI levels. An overweight threshold of 23 (instead of 25) is often cited.
Worked Examples
Adult male
BMI = 26.8 — classified as Overweight (25–29.9). This is a screening result only; further assessment by a healthcare provider is recommended for any clinical decision.
Adult female
BMI = 22.8 — classified as Normal weight (18.5–24.9). In the healthy range per WHO standards.
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Frequently Asked Questions
What is a healthy BMI range?
According to the WHO: Under 18.5 = Underweight, 18.5–24.9 = Normal weight, 25–29.9 = Overweight, 30+ = Obese. BMI is a screening tool, not a diagnostic.
Is BMI accurate?
BMI is a useful screening tool but has limitations. It doesn't account for muscle mass, bone density, age, or where fat is distributed in the body. Athletes may have high BMIs despite low body fat.
Can BMI predict health outcomes?
BMI correlates with health risk at the population level, but individual prediction is imprecise. Two people with the same BMI can have very different health profiles based on diet, fitness, genetics, and fat distribution.
What is the BMI formula in pounds and inches?
BMI = (Weight in pounds ÷ Height in inches²) × 703. For example, 160 lbs at 5'8" (68 inches): (160 ÷ 68²) × 703 = (160 ÷ 4624) × 703 = 24.3.
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