BMI Calculator — Body Mass Index by Age & Sex
This BMI calculator computes your Body Mass Index from height and weight, with interpretation adjusted for age and sex. See your BMI category, healthy weight range, and understand what your score means. BMI is a screening tool, not a medical diagnosis — consult your healthcare provider for personalized advice.
Body Mass Index Calculator
Enter your height and weight to calculate your BMI and see which category you fall into.
Frequently Asked Questions
What is a healthy BMI?
A healthy BMI range is 18.5 to 24.9, classified as "normal weight" by the World Health Organization (WHO). Below 18.5 is underweight, 25.0-29.9 is overweight, and 30.0+ is obese. However, BMI is a screening tool, not a medical diagnosis. Consult your healthcare provider for personalized health assessments.
How do I calculate my BMI?
BMI = weight (kg) / height (m)². For imperial units: BMI = weight (lbs) × 703 / height (inches)². For example, a person weighing 70 kg and 1.75 m tall: BMI = 70 / (1.75)² = 22.9, which falls in the normal weight range.
What is the BMI formula?
The metric formula is BMI = kg/m². The imperial formula is BMI = (lbs × 703) / inches². Both produce the same result. Example: 150 lbs at 5'7" (67 inches) = (150 × 703) / (67 × 67) = 105,450 / 4,489 = 23.5 BMI.
What BMI is considered overweight?
A BMI of 25.0 to 29.9 is classified as overweight by the WHO. For Asian populations, the WHO recommends lower thresholds: 23.0-27.4 is overweight and 27.5+ is obese, due to higher health risks at lower BMI values in these populations.
What BMI is considered obese?
A BMI of 30.0 or higher is classified as obese. There are three obesity classes: Class I (30.0-34.9), Class II (35.0-39.9), and Class III or severe obesity (40.0+). Each class is associated with progressively higher health risks for conditions like type 2 diabetes, heart disease, and certain cancers.
Is BMI accurate for measuring health?
BMI is a useful screening tool but has limitations. It does not distinguish between muscle and fat mass, bone density, or fat distribution. Athletes may have high BMI despite low body fat. Older adults may have misleadingly normal BMI despite muscle loss. For a comprehensive assessment, BMI should be used alongside waist circumference, body fat percentage, and clinical evaluation.
What is a normal BMI for a woman?
The healthy BMI range of 18.5-24.9 applies to both women and men. However, women naturally carry more body fat than men at the same BMI. A BMI of 22 in a woman corresponds to approximately 25-28% body fat, while the same BMI in a man corresponds to approximately 18-22% body fat.
What is a normal BMI for a man?
The same 18.5-24.9 range applies to men. However, men with significant muscle mass (athletes, bodybuilders) may have BMI values in the overweight range (25-29.9) while being perfectly healthy. For muscular men, waist circumference (below 40 inches/102 cm) is a better health indicator.
Does BMI change with age?
The BMI formula stays the same for all adults, but body composition changes with age. Older adults tend to lose muscle mass and gain fat, so a 'normal' BMI may still indicate higher body fat. Some researchers suggest slightly higher BMI ranges (23-28) may be associated with lower mortality in adults over 65.
How is BMI different for children and teens?
For ages 2-19, BMI is calculated the same way but interpreted using CDC age- and sex-specific growth charts as percentiles. Underweight is below the 5th percentile, healthy weight is 5th-85th, overweight is 85th-95th, and obese is at or above the 95th percentile. This accounts for natural body composition changes during growth.
What is BMI Prime?
BMI Prime is your BMI divided by 25 (the upper limit of normal). A BMI Prime of 1.0 means you're at the upper boundary of normal weight. Below 1.0 is underweight or normal; above 1.0 is overweight. For example, a BMI of 27.5 gives a BMI Prime of 1.10, meaning you're 10% above the normal weight upper limit.
Does BMI account for muscle mass?
No, BMI does not differentiate between muscle, fat, bone, or water weight. This is its biggest limitation. A 200-lb person who is 6 feet tall has a BMI of 27.1 regardless of whether that weight is mostly muscle or mostly fat. For athletes and physically active people, body fat percentage or DEXA scans are more accurate measures of body composition.
How to Calculate Your Body Mass Index (BMI)
What is BMI?
Body Mass Index (BMI) is a widely used screening measure that estimates body fat based on a person's height and weight. It was developed by Belgian mathematician Adolphe Quetelet in the 1830s and remains one of the most common tools used by healthcare professionals to assess whether an individual is at a healthy weight.
BMI provides a simple numeric value that places individuals into categories ranging from underweight to obese. While it does not directly measure body fat percentage, it serves as a useful starting point for health assessments and population-level studies.
How to Use This Calculator
- Select your preferred unit system: Imperial (feet, inches, pounds) or Metric (centimeters, kilograms).
- Enter your height using the appropriate fields.
- Enter your weight.
- Click "Calculate BMI" to see your result, category, and where you fall on the BMI scale.
- Use the copy button to save your results for future reference.
BMI Formula
The BMI formula divides weight by the square of height:
BMI = weight (kg) / height (m)²
For imperial units, the conversion is:
- Weight in kg = weight in lbs × 0.453592
- Height in meters = (feet × 12 + inches) × 0.0254
BMI Categories
The World Health Organization (WHO) defines the following BMI categories for adults:
| Category | BMI Range |
|---|---|
| Underweight | < 18.5 |
| Normal weight | 18.5 – 24.9 |
| Overweight | 25.0 – 29.9 |
| Obese Class I | 30.0 – 34.9 |
| Obese Class II | 35.0 – 39.9 |
| Obese Class III | ≥ 40.0 |
Examples
Example 1: Metric Calculation
A person who is 175 cm tall and weighs 70 kg:
BMI = 70 / (1.75)² = 70 / 3.0625 = 22.9 (Normal weight)
Example 2: Imperial Calculation
A person who is 5'10" (70 inches) and weighs 180 lbs:
Height in meters = 70 × 0.0254 = 1.778 m
Weight in kg = 180 × 0.453592 = 81.6 kg
BMI = 81.6 / (1.778)² = 81.6 / 3.161 = 25.8 (Overweight)
Use Cases
- Health Screening: Quickly assess whether your weight is within a healthy range during routine health checkups.
- Fitness Goals: Track your BMI over time as part of a weight management or fitness program.
- Population Studies: Researchers use BMI to study obesity trends and health outcomes across large groups.
- Insurance Assessments: Some insurers use BMI as one factor when evaluating health risk profiles.
- Clinical Reference: Healthcare providers use BMI alongside other metrics to evaluate overall health.
Tips and Limitations
While BMI is a useful screening tool, it has important limitations to keep in mind:
- BMI does not distinguish between muscle mass and fat mass. Athletes with high muscle mass may have a high BMI despite being lean.
- Age, gender, and ethnicity can influence the relationship between BMI and body fat.
- BMI is not recommended as the sole diagnostic tool for determining health status.
- For a more complete picture, consider combining BMI with waist circumference, body fat percentage, and other health indicators.
- Consult a healthcare professional for personalized health advice based on your individual circumstances.
BMI categories are designed for adults aged 20 and older. For children and teenagers, BMI is interpreted differently using age-specific and sex-specific percentile charts.
BMI Categories Reference Table
| Category | BMI Range | Asian BMI Range | Health Risk |
|---|---|---|---|
| Severe Thinness | < 16.0 | < 16.0 | Severe |
| Moderate Thinness | 16.0 - 16.9 | 16.0 - 16.9 | Moderate |
| Mild Thinness | 17.0 - 18.4 | 17.0 - 18.4 | Low |
| Normal Weight | 18.5 - 24.9 | 18.5 - 22.9 | Minimal |
| Overweight | 25.0 - 29.9 | 23.0 - 27.4 | Increased |
| Obese Class I | 30.0 - 34.9 | 27.5 - 32.4 | High |
| Obese Class II | 35.0 - 39.9 | 32.5 - 37.4 | Very High |
| Obese Class III | ≥ 40.0 | ≥ 37.5 | Extremely High |
Asian BMI thresholds are recommended by WHO for populations of South Asian, Chinese, and Japanese descent due to higher health risks at lower BMI values.
Healthy Weight Range by Height
The following table shows the healthy weight range (BMI 18.5-24.9) for common heights.
| Height | Min Weight (BMI 18.5) | Max Weight (BMI 24.9) |
|---|---|---|
| 5'0" (152 cm) | 95 lbs (43 kg) | 128 lbs (58 kg) |
| 5'2" (157 cm) | 101 lbs (46 kg) | 136 lbs (62 kg) |
| 5'4" (163 cm) | 108 lbs (49 kg) | 145 lbs (66 kg) |
| 5'6" (168 cm) | 115 lbs (52 kg) | 154 lbs (70 kg) |
| 5'8" (173 cm) | 122 lbs (55 kg) | 164 lbs (74 kg) |
| 5'10" (178 cm) | 129 lbs (59 kg) | 174 lbs (79 kg) |
| 6'0" (183 cm) | 136 lbs (62 kg) | 184 lbs (83 kg) |
| 6'2" (188 cm) | 144 lbs (65 kg) | 194 lbs (88 kg) |
| 6'4" (193 cm) | 152 lbs (69 kg) | 204 lbs (93 kg) |
Important Health Disclaimer
This calculator is for informational purposes only.
- BMI is a screening tool, not a medical diagnosis.
- It does not distinguish between muscle mass, bone density, and body fat.
- BMI may not accurately reflect health for athletes, elderly, pregnant women, or certain ethnic groups.
- Consult your healthcare provider for personalized health assessments and medical advice.
Data sources: World Health Organization (WHO), Centers for Disease Control and Prevention (CDC), National Institutes of Health (NIH).
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