BMI Calculator
Calculate Body Mass Index for adults and children. Free, fast, and accurate.
BMI Calculator
Calculate Body Mass Index for adults and children
What is BMI?
Body Mass Index (BMI) is a numerical value calculated from your weight and height. It is one of the most commonly used screening tools to estimate whether a person's weight is in a healthy range. First developed by Belgian mathematician Adolphe Quetelet in the 1830s, BMI remains a standard health indicator used by the World Health Organization (WHO) and the Centers for Disease Control and Prevention (CDC).
BMI provides a quick, inexpensive, and non-invasive way to categorize individuals into weight status categories. For adults, BMI is interpreted using standard categories that apply to both men and women. For children and teens aged 2 to 19, BMI is interpreted differently — it is compared against age-and-sex-specific growth charts to determine a percentile ranking.
While BMI is not a direct measure of body fat and does not distinguish between muscle, bone, and fat, it correlates well with more direct measures of body fat. It is widely used in clinical settings, public health research, and fitness assessments to identify potential health risks associated with being underweight or overweight.
Key Fact: A BMI between 18.5 and 24.9 is generally considered healthy for adults. Being above or below this range may indicate increased health risks.
How to Calculate BMI
Body Mass Index (BMI) is a simple calculation using a person's height and weight. It is the most widely used method for estimating body fat and categorizing weight status.
BMI = Weight (kg) ÷ Height² (m²)
Metric example: A person who is 170 cm (1.70 m) tall and weighs 65 kg:
- Convert height to meters: 170 cm = 1.70 m
- Square the height: 1.70² = 2.89
- Divide weight by height squared: 65 ÷ 2.89 = 22.5
- BMI = 22.5 (Normal weight)
US example: A person who is 5'10" (70 inches) and weighs 160 lbs:
- Multiply weight by 703: 160 × 703 = 112,480
- Square the height in inches: 70² = 4,900
- Divide: 112,480 ÷ 4,900 = 22.96
- BMI = 23.0 (Normal weight)
Our calculator above handles both unit systems automatically. Simply enter your height and weight, and get your BMI with a visual chart showing where you fall in the BMI categories.
Adult BMI Categories (WHO)
The World Health Organization recommends the following BMI classifications for adults aged 20 and older:
| 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 |
BMI Chart for Adults
This chart shows BMI categories based on height and weight. Find your height on the left column, then look across to see which weight range places you in each BMI category.
Child & Teen BMI (Ages 2–19)
For children and teens, BMI is interpreted differently than for adults. Because body composition changes with age and varies between boys and girls, BMI is compared to age-and-sex-specific percentile charts from the Centers for Disease Control and Prevention (CDC).
Our calculator uses CDC BMI-for-age data to determine the percentile and weight status category. Age and sex are required for child/teen calculations.
| Category | Percentile Range |
|---|---|
| Underweight | < 5th percentile |
| Healthy Weight | 5th – 85th percentile |
| At Risk of Overweight | 85th – 95th percentile |
| Overweight | ≥ 95th percentile |
BMI Risks and Limitations
Risks of Being Overweight
- High blood pressure
- Type 2 diabetes
- Heart disease and stroke
- Sleep apnea
- Joint problems
Risks of Being Underweight
- Malnutrition
- Weakened immune system
- Bone density loss
- Growth issues in children
- Fertility problems
Limitations of BMI: While BMI is a useful screening tool, it does not directly measure body fat. It cannot distinguish between muscle mass and fat mass. Athletes and muscular individuals may have a high BMI due to muscle weight rather than excess fat. Older adults tend to have more body fat than younger people with the same BMI. Women generally have more body fat than men at an equivalent BMI.
For children, BMI is a better indicator of excess body fat for obese children than for overweight children. Height and sexual maturation can influence BMI during growth years. For a complete health assessment, BMI should be used alongside other measurements. Consult a healthcare professional for personalized guidance.
Frequently Asked Questions
What is BMI?
How do I calculate BMI?
What is a healthy BMI range for adults?
How is BMI different for children and teens?
Is BMI accurate for everyone?
References
- 1.World Health Organization (WHO).Obesity and Overweight — Fact Sheet.
The BMI calculator on this page is for informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider for personalized guidance.
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