BMI Calculator
Calculate your Body Mass Index (BMI) instantly. Enter your height and weight below — supports both imperial and metric units — to see your BMI score and weight category.
What Is BMI?
Body Mass Index (BMI) is a numerical value derived from a person's weight and height. First developed by Belgian mathematician Adolphe Quetelet in the 1830s, BMI is now used worldwide by healthcare professionals as a quick screening tool to identify possible weight-related health risks.
While BMI does not directly measure body fat, research has shown that BMI correlates reasonably well with direct measures of body fat for most adults. It is inexpensive, non-invasive, and requires only two measurements, making it practical for large-scale health assessments.
BMI Categories Explained
| BMI Range | Category | Health Risk |
|---|---|---|
| Below 18.5 | Underweight | Nutritional deficiency, osteoporosis |
| 18.5 – 24.9 | Normal weight | Lowest health risk |
| 25 – 29.9 | Overweight | Moderate risk of chronic disease |
| 30 and above | Obese | High risk of heart disease, type 2 diabetes |
The BMI Formula
BMI is calculated using one of these two formulas depending on your unit system:
Metric
BMI = weight (kg) ÷ height² (m)Imperial
BMI = (weight (lbs) × 703) ÷ height² (inches)For example, a person who is 5'9" (175 cm) and weighs 160 lbs (72.6 kg) has a BMI of approximately 23.6 — within the normal weight range.
Frequently Asked Questions
- What is a healthy BMI range for adults?
- For adults 20 and older, a BMI between 18.5 and 24.9 is considered normal or healthy weight. A BMI below 18.5 is classified as underweight, 25–29.9 as overweight, and 30 or above as obese. These ranges are the same for men and women.
- Is BMI an accurate measure of body fat?
- BMI is a useful screening tool but has limitations. It does not directly measure body fat — it estimates it from weight and height. Athletes with high muscle mass may have a high BMI without excess fat, while older adults may have a normal BMI with a higher percentage of body fat. Always discuss your results with a healthcare provider.
- What is the BMI formula?
- BMI is calculated by dividing weight in kilograms by the square of height in meters: BMI = weight (kg) ÷ height² (m). In imperial units: BMI = (weight in pounds × 703) ÷ height² (inches).
- How is BMI calculated differently for children?
- For children and teens aged 2–19, BMI is calculated the same way but interpreted using age- and sex-specific percentile charts rather than fixed cutoffs. A BMI at or above the 95th percentile for age and sex is classified as obese.
- What should I do if my BMI is outside the normal range?
- BMI is one indicator among many. If your BMI falls outside the normal range, consult a physician or registered dietitian who can perform a comprehensive assessment including body composition, waist circumference, diet, activity level, and medical history before recommending any changes.