BMI Calculator
Use this free body mass index calculator to calculate your BMI instantly. Enter your height and weight to see your BMI score, category, healthy weight range, and position on the BMI chart. Works with metric (kg, cm) and imperial (lb, in) units. No signup required.
—
Enter height and weight above
Your BMI on the chart
How to use this BMI calculator
- Choose metric (kg and cm) or imperial (lb and in).
- Enter your weight and height.
- Your BMI score and category update automatically.
- Check the BMI chart to see where your result falls.
For the most consistent results, measure height and weight at the same time of day, without shoes, and use accurate values.
What is BMI?
Body Mass Index (BMI) is a number calculated from your weight and height. It is used as a screening tool to estimate whether an adult is underweight, normal weight, overweight, or obese. A BMI calculator does not measure body fat directly, but it is a fast way to check whether your weight may be in a healthy range for your height.
How to calculate BMI
Metric formula:
BMI = weight (kg) ÷ [height (m)]²
Example (metric): 70 kg and 175 cm (1.75 m) → 70 ÷ 1.75² = 22.9 (normal weight)
Imperial formula:
BMI = 703 × weight (lb) ÷ [height (in)]²
Example (imperial): 154 lb and 68 in → 703 × 154 ÷ 68² = 23.4 (normal weight)
If you measure height in feet and inches, convert to total inches first (e.g. 5 ft 8 in = 68 in).
BMI calculator with imperial units (lb & in)
In the United States and other countries that use imperial measurements, BMI is often calculated with pounds (lb) and inches (in). Select Imperial in the calculator above, enter your weight in pounds and your total height in inches, and your BMI is computed automatically.
BMI Categories (Adults)
These BMI categories apply to most adults aged 18 and older.
| BMI Range | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Normal weight |
| 25 – 29.9 | Overweight |
| 30 or higher | Obesity |
These categories may not be accurate for children, athletes, very muscular individuals, or older adults.
Healthy BMI ranges by age (general guidance)
While BMI categories are the same for all adults, body composition naturally changes with age. The ranges below are general population averages, not medical standards.
| Age group | Typical healthy BMI |
|---|---|
| 18–24 | 19–24 |
| 25–34 | 20–25 |
| 35–44 | 21–26 |
| 45–54 | 22–27 |
| 55–64 | 23–28 |
| 65+ | 24–29 |
Healthy BMI by Age (Visual Chart)
Limitations of BMI
BMI is useful for population-level screening, but it has important limitations:
- Does not measure body fat directly — it is based only on height and weight.
- Does not account for muscle mass — athletes may appear “overweight” despite low body fat.
- Does not consider age or sex differences in body composition.
- Does not reflect fat distribution — waist size and where fat is stored also matter.
- Not ideal for children, seniors, or very muscular individuals.
Because of these limitations, BMI should be viewed as a starting point, not a complete picture of health.
Alternatives and complements to BMI
Other measurements can provide a more complete view of health and body composition:
Body fat percentage
Body fat percentage can be estimated using calipers, smart scales, or more advanced methods like DEXA scans. It gives a more direct measure of how much of your body is fat versus lean mass.
Waist-to-height ratio
Waist-to-height ratio is a strong predictor of metabolic and cardiovascular risk. A common guideline is:
Waist-to-height ratio = waist (cm) ÷ height (cm)
Many sources suggest aiming for a value below 0.5.
Waist circumference
Higher waist measurements are associated with increased health risks, even at a “normal” BMI. Common risk thresholds include:
- Men: more than 40 inches (102 cm)
- Women: more than 35 inches (88 cm)
How to improve your BMI safely
If your BMI is outside the normal range, small, sustainable changes can help improve your health over time:
- Focus on a balanced diet with whole foods.
- Include regular physical activity, such as walking, cycling, or swimming.
- Add strength training to build muscle and improve body composition.
- Prioritize sleep and stress management.
- Stay hydrated and avoid excessive sugary drinks.
For personalized advice, always speak with a qualified healthcare professional.
BMI Calculator FAQ
How do I calculate my BMI?
Divide your weight by your height squared. In metric: kg ÷ (m)². In imperial: 703 × lb ÷ (in)². Use the calculator above to do it instantly.
What is a normal BMI?
For most adults, a BMI between 18.5 and 24.9 is considered normal weight.
What does my BMI number mean?
Your BMI places you in a category: underweight (below 18.5), normal (18.5–24.9), overweight (25–29.9), or obesity (30+). It is a screening result, not a diagnosis.
Is this BMI calculator free?
Yes. This online body mass index calculator is completely free and requires no account.
Is BMI a perfect measure of health?
No. BMI is a simple screening tool and does not measure body fat, fitness level, or overall health. It should be interpreted alongside other information.
Is BMI accurate for athletes?
Not always. People with high muscle mass may have a higher BMI even if their body fat is low.
Should I rely only on BMI?
No. BMI should not be used as the sole indicator of health. A healthcare professional can provide a more complete assessment.
How do I calculate BMI with imperial units?
Use the formula: BMI = 703 × weight (lb) ÷ [height (in)]². Select Imperial in the calculator and enter pounds and total inches.
Can BMI be wrong?
Yes. Because it does not account for muscle, age, sex, or fat distribution, BMI can misclassify some individuals.
Medical disclaimer
This BMI calculator and the information on this page are for general educational purposes only and are not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider with any questions about your health, weight, or BMI.