BMI Calculator
The Body Mass Index (BMI) is one of the most widely used tools for assessing whether an individual has a healthy body weight relative to their height. While it isn't a perfect measure, it provides a quick and easy screening tool.
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About the BMI Calculator
The Body Mass Index (BMI) is one of the most widely used screening tools for assessing healthy body weight relative to height. Developed in the 19th century by Belgian mathematician Adolphe Quetelet, BMI provides a quick, free, and non-invasive way to estimate whether a person falls in an underweight, normal, overweight, or obese range.
Our free BMI calculator supports both metric units (centimetres and kilograms) and US imperial units (feet, inches, and pounds), making it suitable for users in the United States, United Kingdom, Canada, Australia, and worldwide.
BMI Formula
Metric Formula
BMI = Weight (kg) ÷ Height² (m)
Example: 70 kg ÷ (1.75 × 1.75) = 22.9
Imperial Formula
BMI = 703 × Weight (lbs) ÷ Height² (in)
Example: 703 × 154 ÷ (69 × 69) = 22.7
BMI Classification Chart for Adults
| Classification | BMI Range (kg/m²) |
|---|---|
| Severe Thinness | < 16 |
| Moderate Thinness | 16 – 17 |
| Mild Thinness | 17 – 18.5 |
| Normal | 18.5 – 25 |
| Overweight | 25 – 30 |
| Obese Class I | 30 – 35 |
| Obese Class II | 35 – 40 |
| Obese Class III | > 40 |
Source: World Health Organization (WHO) BMI classification standards.
BMI for Different Groups
BMI Calculator for Women
Women naturally carry 6–11% more body fat than men at the same BMI. A healthy BMI range of 18.5–24.9 applies to women, but waist circumference under 35 inches (88 cm) is equally important. Postmenopausal women should monitor BMI more frequently due to hormonal fat redistribution.
BMI Calculator for Men
Men typically have higher muscle mass, which can raise BMI without excess fat. A BMI of 18.5–24.9 is healthy for men. Waist circumference over 40 inches (102 cm) signals abdominal obesity risk regardless of overall BMI score.
BMI for Seniors (65+)
Older adults often lose muscle mass (sarcopenia), so BMI can underestimate body fat. Many doctors consider a BMI of 23–27 acceptable for those over 65. Body composition testing is recommended for a more accurate health assessment in seniors.
BMI for Children & Teens
For children aged 2–19, BMI is calculated the same way but interpreted using age- and sex-specific percentile charts (CDC growth charts). A BMI at or above the 95th percentile is classified as obese. Use a dedicated paediatric BMI calculator for accurate results.
Limitations of BMI
While BMI is a useful population-level screening tool, it has important limitations that every user should be aware of:
- •Does not measure body fat directly — BMI cannot distinguish between muscle mass and fat mass. A muscular athlete may be classified as overweight despite having very low body fat percentage.
- •Does not account for fat distribution — Abdominal (visceral) fat is more metabolically dangerous than fat stored in the hips or thighs. Waist circumference is a better predictor of cardiovascular risk.
- •Race and ethnicity differences — South Asian and East Asian populations face higher health risks at lower BMI values. The WHO recommends adjusted thresholds for Asian populations (overweight at BMI ≥ 23).
- •Not a standalone diagnostic tool — Always consult a qualified healthcare professional before drawing health conclusions from BMI alone. BMI is a screening metric, not a diagnosis.
Frequently Asked Questions
For adults aged 18–65, a healthy BMI is between 18.5 and 24.9 kg/m². A BMI below 18.5 is underweight, 25–29.9 is overweight, and 30 or above is classified as obese. Maintaining a healthy BMI reduces the risk of heart disease, type 2 diabetes, and joint problems.
No, BMI can be misleading for athletes and highly muscular individuals. Since muscle tissue is denser than fat, a muscular person may show a high BMI despite having very low body fat. In such cases, tools like DEXA scan, body fat percentage measurement, or waist-to-hip ratio offer more accurate health assessments.
Yes, the standard WHO BMI scale uses identical ranges for men and women. However, women naturally carry 6–11% more body fat than men at the same BMI. Some clinicians recommend also measuring waist circumference or body fat percentage for a more complete picture of health.
If your BMI is 25 or above, consult a healthcare provider for personalised advice. General steps include adopting a calorie-balanced diet rich in vegetables, whole grains, and lean proteins; engaging in at least 150 minutes of moderate aerobic activity per week; improving sleep quality; and managing stress. Small, consistent changes lead to lasting results.
For children and teens aged 2–19, BMI is calculated using the same formula as adults but is interpreted using age- and sex-specific growth charts (CDC or WHO). A BMI at or above the 95th percentile for age and sex is classified as obese in children. Always use a dedicated paediatric BMI calculator for accurate results.
The BMI formula remains the same across age groups, but its interpretation may vary for adults over 65. Older adults tend to lose muscle mass and bone density, so their BMI may appear normal while they carry excess body fat. A BMI of 23–27 is often considered acceptable for seniors, and doctors may recommend body composition testing.
For women, a BMI between 18.5 and 24.9 is considered healthy. Women generally have higher body fat percentages than men at the same BMI, so waist circumference (below 35 inches or 88 cm) is also an important health marker. Postmenopausal women are at higher risk of weight gain and should monitor BMI regularly.
BMI is a population-level screening tool, not a definitive health diagnostic. High BMI is associated with increased risk of type 2 diabetes, cardiovascular disease, sleep apnea, and certain cancers. However, a person with normal BMI can still have metabolic risk factors. A comprehensive health evaluation includes blood pressure, blood glucose, cholesterol levels, and lifestyle factors.
In metric units: BMI = Weight (kg) ÷ Height² (m). Example: if you weigh 70 kg and are 1.75 m tall, BMI = 70 ÷ (1.75 × 1.75) = 22.9. In imperial units: BMI = 703 × Weight (lbs) ÷ Height² (inches). Example: 703 × 154 ÷ (69 × 69) = 22.7.
A BMI of 30 or above is classified as obesity, divided into Class I (30–34.9), Class II (35–39.9), and Class III (40+, severe obesity). At this level, health risks increase significantly — including a 2–4x higher risk of type 2 diabetes, high blood pressure, heart disease, and sleep apnea. Medical supervision is recommended for weight management.
About the BMI Calculator
The Body Mass Index (BMI) is one of the most widely used tools for assessing whether an individual has a healthy body weight relative to their height. While it isn't a perfect measure, it provides a quick and easy screening tool.
Formula
BMI Classification Table
| Classification | BMI Range (kg/m²) |
|---|---|
| Severe Thinness | < 16 |
| Moderate Thinness | 16 – 17 |
| Mild Thinness | 17 – 18.5 |
| Normal | 18.5 – 25 |
| Overweight | 25 – 30 |
| Obese Class I | 30 – 35 |
| Obese Class II | 35 – 40 |
| Obese Class III | > 40 |