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BMI Calculator

Calculate your Body Mass Index (BMI) using height and weight. See your BMI category and healthy weight range.

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Understanding BMI: Body Mass Index Explained

Body Mass Index (BMI) is a simple screening tool that estimates body fat based on height and weight. It was developed in the 1830s by Belgian mathematician Adolphe Quetelet and is still widely used by healthcare providers as a quick assessment tool.

How BMI Is Calculated

The formula is straightforward:

Metric: BMI = weight (kg) / height (m)²
Imperial: BMI = (weight (lbs) × 703) / height (in)²

BMI Categories

The World Health Organization defines four main categories:

Underweight: BMI below 18.5
Normal weight: BMI 18.5 to 24.9
Overweight: BMI 25.0 to 29.9
Obese: BMI 30.0 and above (further divided into Class I, II, and III)

What BMI Does Not Measure

BMI is a useful population-level metric, but it has significant limitations at the individual level:

Muscle vs. fat: BMI does not distinguish between muscle mass and fat mass. A muscular athlete may have a "overweight" BMI despite having low body fat.
Fat distribution: Where fat is stored matters. Visceral fat (around organs) poses greater health risks than subcutaneous fat (under the skin), but BMI does not account for this.
Age and sex: Women naturally carry more body fat than men. Older adults tend to have more fat and less muscle. Standard BMI categories do not adjust for these differences.
Ethnicity: Research shows that health risks associated with a given BMI differ across ethnic groups. For example, some Asian populations face increased health risks at lower BMI thresholds.

Better Alternatives to BMI

For a more complete picture of health, consider these additional metrics: waist circumference, waist-to-hip ratio, body fat percentage (measured via DEXA scan, bioelectrical impedance, or skinfold calipers), and waist-to-height ratio. Many health professionals now use BMI as a starting point alongside other assessments rather than as a standalone diagnostic tool.

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How to Use the BMI Calculator

1
Enter your height
Input your height using either feet and inches or centimeters, depending on your preferred unit system.
2
Enter your weight
Input your body weight in pounds or kilograms.
3
Select the unit system
Choose between imperial (feet, pounds) or metric (centimeters, kilograms) units for your measurements.
4
View your BMI category
Review your calculated BMI score and see which category it falls into: underweight, normal weight, overweight, or obese.

Sources & Verification

CDC BMI Information

Published by ConvertCrunch Editorial Team | Our Methodology

Frequently Asked Questions

What is BMI and how is it calculated?

BMI (Body Mass Index) is a screening tool that estimates body fat based on height and weight. The formula is weight in kilograms divided by height in meters squared. In imperial units, it is (weight in pounds times 703) divided by (height in inches squared). A person weighing 70 kg at 175 cm tall has a BMI of 22.9. The WHO classifies BMI as: underweight (below 18.5), normal weight (18.5-24.9), overweight (25-29.9), and obese (30 and above).

Is BMI an accurate measure of health?

BMI is a useful population-level screening tool but has significant limitations for individuals. It does not distinguish between muscle and fat, so athletic individuals may be classified as overweight despite having low body fat. It does not account for age, sex, ethnicity, or fat distribution. Waist circumference, waist-to-hip ratio, body fat percentage, and metabolic markers (blood pressure, blood sugar, cholesterol) provide a more complete health picture. Consult a healthcare professional for a comprehensive assessment.

What is a healthy BMI range?

The World Health Organization defines a healthy BMI as 18.5 to 24.9 for adults. However, optimal ranges vary by ethnicity: the WHO suggests lower cutoff points for Asian populations (overweight at 23, obese at 27.5) due to higher metabolic risk at lower BMIs. For older adults over 65, a slightly higher BMI of 25-27 may be associated with lower mortality risk. For children and teenagers, BMI is interpreted using age-specific and sex-specific percentile charts rather than fixed cutoffs.

How can I use BMI alongside other health metrics?

Use BMI as a starting point, then supplement with waist circumference (above 40 inches for men or 35 inches for women indicates higher risk), body fat percentage (measured via DEXA scan, bioimpedance, or skinfold calipers), waist-to-hip ratio, blood pressure, fasting blood glucose, and cholesterol levels. Two people with identical BMIs can have very different health profiles depending on muscle mass, fat distribution, fitness level, and metabolic health. A doctor can help interpret these metrics together.

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