The formula this calculator uses
Body Mass Index (metric)
BMI = Weight (kg) ÷ (Height (m) × Height (m))
Example: 65 kg, 170 cm (1.70 m) → 65 ÷ (1.70 × 1.70) = 65 ÷ 2.89 = 22.5
Body Mass Index (imperial)
BMI = (Weight (lbs) × 703) ÷ (Height (in) × Height (in))
Example: 143 lbs, 5'7" (67 in) → (143 × 703) ÷ (67 × 67) = 100,529 ÷ 4,489 = 22.4
What BMI actually measures
Body Mass Index is a simple screening number that compares a person's weight to their height, developed in the 1830s as a population-level statistic rather than an individual diagnostic tool. It was never designed to measure body fat directly — it's a ratio, and ratios can't tell the difference between a kilogram of muscle and a kilogram of fat. Despite that limitation, BMI remains widely used by doctors and health organizations because it's quick to calculate, requires no special equipment, and correlates reasonably well with health risk across large populations.
The standard BMI categories
Most health organizations use the same broad bands for adults: below 18.5 is classed as underweight, 18.5 to 24.9 as a healthy weight range, 25 to 29.9 as overweight, and 30 or above as obese, sometimes split further into class 1, 2, and 3. These bands were built from large population studies linking BMI to health outcomes, but they're general guidelines rather than a personal verdict — two people with an identical BMI can have very different amounts of muscle, fat, and overall health.
BMI Chart for Adults
Use the following BMI chart to quickly identify your category based on your BMI score:
| BMI Range | Category | Health Risk |
|---|---|---|
| Below 18.5 | Underweight | Moderate to severe risk of malnutrition |
| 18.5 – 24.9 | Healthy Weight | Low risk |
| 25.0 – 29.9 | Overweight | Increased risk |
| 30.0 – 34.9 | Obese Class I | High risk |
| 35.0 – 39.9 | Obese Class II | Very high risk |
| 40.0 and above | Obese Class III | Extremely high risk |
Where BMI falls short
Because BMI can't separate muscle from fat, it tends to overestimate body fat in muscular people, such as athletes and bodybuilders, and can underestimate it in people who have lost muscle mass, which is common in older adults. It also doesn't account for where fat is distributed on the body, which matters for health risk, or for differences between sexes, ethnic groups, and body frame sizes. For these reasons, BMI is best treated as a starting point for a conversation with a healthcare provider, not a final answer on its own.
BMI for Men vs Women
The BMI formula is identical for men and women. However, women naturally tend to carry a higher percentage of body fat than men at the same BMI. This means a woman with a BMI of 22 may have more body fat than a man with the same BMI. Because of these physiological differences, some health professionals use BMI alongside other measures like waist circumference and body fat percentage for a more accurate assessment.
BMI for Teenagers and Children
BMI is calculated the same way for children and teenagers, but the results are interpreted differently. Instead of using fixed adult categories, a child's BMI is plotted on age- and sex-specific growth charts to determine their percentile. A teenager at the 85th percentile is considered overweight, while one at the 95th percentile or above is considered obese. This is because body composition changes rapidly during growth, and what is normal at age 10 differs from what is normal at age 16.
How to use this calculator
- Select your preferred unit system: Metric (cm/kg) or Imperial (ft/in, lbs).
- Enter your height in the selected unit.
- Enter your weight in the selected unit.
- Your BMI, category, and visual indicator update instantly.
What to do after calculating your BMI?
BMI is just one piece of the puzzle. To get a complete picture of your health, you might also want to:
- Calculate your daily calorie needs with our Calorie Calculator.
- Track your workout and rest intervals with our Time Calculator.
- Check your body fat percentage using a dedicated Body Fat Calculator.
Frequently asked questions
How is BMI calculated?
BMI = weight in kilograms divided by height in meters squared. For pounds and inches, multiply weight by 703 and divide by height in inches squared.
What is a normal BMI?
A normal BMI for most adults falls between 18.5 and 24.9. This range is associated with the lowest risk of weight-related health conditions such as diabetes and heart disease.
What is 170 cm with 70 kg BMI?
A person who is 170 cm tall and weighs 70 kg has a BMI of 24.2. This falls within the healthy weight range (18.5 to 24.9), though it is close to the overweight threshold of 25.
What is the BMI formula?
The BMI formula is: BMI = weight (kg) ÷ (height (m) × height (m)). For imperial units: BMI = (weight (lbs) × 703) ÷ (height (in) × height (in)).
Is a BMI of 26 chubby?
A BMI of 26 falls into the overweight category (25 to 29.9). However, whether it looks 'chubby' depends on muscle mass, body composition, and frame size. BMI is a screening tool, not a visual assessment.
Is BMI different for males and females?
The BMI formula is the same for both males and females. However, females naturally tend to have a higher percentage of body fat than males at the same BMI. This means the same BMI value may represent different levels of body fat in men and women.
What is the BMI for a teenager?
For children and teenagers (ages 2 to 19), BMI is calculated using the same formula but interpreted differently. It is compared against age- and sex-specific percentile charts rather than the adult BMI categories. A teenager's BMI is classified as underweight, healthy, overweight, or obese based on their percentile.
Can I use BMI calculator with age?
The standard BMI calculator is designed for adults (age 18 and above). For children and teenagers, a BMI-for-age percentile calculator is required because body composition changes rapidly during growth. For older adults, BMI may underestimate body fat due to muscle loss.
What is the BMI calculator for female?
The BMI calculator for females uses the same formula as for males: weight (kg) ÷ (height (m) × height (m)). However, because women naturally have more body fat than men at the same BMI, the results should be interpreted with that in mind. Some health professionals recommend combining BMI with waist circumference for a more accurate assessment in women.
What is the BMI calculator for male?
The BMI calculator for males uses the standard formula: weight (kg) ÷ (height (m) × height (m)). Men typically have more muscle mass than women, which can push BMI higher without indicating excess fat. Athletes and bodybuilders may have a high BMI despite low body fat.
Is BMI accurate for everyone?
No. BMI doesn't distinguish between muscle and fat, so it can be misleading for athletes, older adults, pregnant women, and some other groups.
Is BMI a medical diagnosis?
No. BMI is a general screening tool, not a diagnosis. A doctor should be consulted for a full assessment of health and body composition.