BMI Calculator
Use this free BMI calculator to find your Body Mass Index in metric (kg and cm) or imperial (lb and inches) units. Along with your BMI number, you will see the standard adult category it falls into, so you can understand your result at a glance.
What Is BMI?
Body Mass Index is a simple measure that compares your weight to your height. It is widely used as a quick screening tool because it needs only two measurements and no special equipment. BMI does not measure body fat directly, but for many adults it gives a reasonable first indication of whether weight is in a typical range for their height.
The BMI Formula
- Metric: BMI = weight (kg) ÷ height (m)²
- Imperial: BMI = 703 × weight (lb) ÷ height (in)²
Example: someone who weighs 70 kg and is 1.75 m tall has a BMI of 70 ÷ (1.75 × 1.75) ≈ 22.9.
Adult BMI Categories
- Below 18.5 — Underweight
- 18.5 to 24.9 — Normal weight
- 25.0 to 29.9 — Overweight
- 30.0 and above — Obese
These ranges are the commonly used adult categories from the World Health Organization. Some health bodies use slightly different cut-offs for certain populations, so your doctor may interpret your number with additional context.
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Limitations of BMI
BMI is a useful starting point, but it has blind spots. It cannot tell the difference between muscle and fat, so athletes and very muscular people may be classed as overweight even when their body fat is low. It also does not show where fat is stored, which matters for health. Older adults may have less muscle, meaning a normal BMI can hide higher body fat.
For a fuller picture, health professionals often combine BMI with waist measurement, blood pressure, blood tests and lifestyle factors. Treat your BMI as one piece of information rather than a final verdict.
Children and Teenagers
For children and teens, BMI is interpreted differently. Instead of fixed categories, results are compared with growth charts for the same age and sex, and expressed as a percentile. The adult categories above should not be used for people under 18.
Next Steps After Checking Your BMI
If you want to adjust your weight, knowing how much energy your body uses is helpful. The calorie calculator estimates your daily needs using BMR and TDEE. You can also track milestones by date with the age calculator.
Disclaimer: This BMI calculator is for general information only and is not medical advice. Please talk to a doctor or qualified health professional before making decisions about your health, diet or exercise.
Frequently Asked Questions
What is BMI and how is it calculated?
BMI, or Body Mass Index, compares weight to height. In metric units it is weight in kilograms divided by height in metres squared. In imperial units it is 703 multiplied by weight in pounds, divided by height in inches squared. The result places adults in a general weight category.
What is a healthy BMI range for adults?
For most adults, a BMI between 18.5 and 24.9 is considered the normal range. Below 18.5 is underweight, 25 to 29.9 is overweight and 30 or above is obese. A doctor may use different thresholds depending on age, ethnicity and overall health.
Is BMI accurate for athletes and muscular people?
Not always. BMI cannot distinguish muscle from fat, so muscular people can have a high BMI while having low body fat. For athletes, measures like waist circumference or body composition tests usually give a more meaningful picture than BMI alone.
How do I calculate BMI in pounds and inches?
Multiply your weight in pounds by 703, then divide by your height in inches squared. For example, 160 lb at 68 inches gives 703 × 160 ÷ (68 × 68) ≈ 24.3. Switching the calculator to imperial units does this automatically.
Is BMI different for men, women and children?
For adults, the same formula and categories are used for men and women, although body fat levels at the same BMI can differ. For children and teens, BMI is compared to age- and sex-specific growth charts and reported as a percentile.