BMI Calculator
Enter your height and weight to get your BMI, WHO weight category, and a healthy weight range, in metric or imperial units.
Formula verified July 2026
Your BMI
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How this BMI calculator works
Enter your height and weight in metric or imperial units to get your Body Mass Index, its WHO weight category, and the healthy weight range for your height. BMI is a quick screening tool, not a full health diagnosis.
The BMI formula
- Metric: BMI = weight in kg ÷ (height in meters)²
- Imperial: BMI = (weight in lb ÷ (height in inches)²) × 703
WHO BMI categories
| BMI range | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Normal weight |
| 25.0 – 29.9 | Overweight |
| 30.0 and above | Obesity |
Step-by-step: how to calculate your BMI
- Convert your height to meters (metric) or leave it in inches (imperial).
- Square your height (multiply it by itself).
- Divide your weight by that squared height figure.
- For imperial units, multiply the result by 703 to get a comparable BMI value.
- Compare the result to the WHO category table above.
Worked example
A person who is 170 cm (1.70 m) tall and weighs 68 kg:
- Height squared: 1.70 × 1.70 = 2.89
- BMI: 68 ÷ 2.89 = 23.5
- Category: Normal weight (falls between 18.5 and 24.9)
- Healthy weight range for this height: approximately 53.5 kg to 72.0 kg
Common BMI mistakes
- Treating BMI as a complete health assessment. It doesn’t distinguish between muscle mass and fat mass.
- Applying adult BMI categories to children, who require age- and sex-specific growth charts instead.
- Mixing unit systems, like entering height in inches but weight in kilograms, which produces a meaningless result.
- Over-interpreting small differences a BMI of 24.8 versus 25.1 crosses a category line but represents a tiny real-world difference.
Limitations of BMI
- Athletes and muscular individuals often show a higher BMI despite low body fat.
- BMI doesn’t account for where fat is distributed on the body, which matters for health risk.
- It’s a population-level screening tool, not a personalized medical diagnosis.
- Always discuss your results with a healthcare provider before making health decisions based on BMI alone.
Is BMI accurate for everyone?
BMI is a useful population-level screening tool but has known limitations for athletes, older adults, pregnant women, and people with unusually high muscle mass, since it can’t distinguish between muscle and fat.
What’s a healthy BMI range?
According to the World Health Organization, a BMI between 18.5 and 24.9 falls in the normal weight range for most adults.
Does this calculator work for children?
No. Children and teenagers need age- and sex-specific BMI percentile charts rather than the fixed adult categories used here. Consult a pediatrician for a child’s growth assessment.
How is BMI different from body fat percentage?
BMI is calculated from height and weight only and doesn’t measure body composition directly. Body fat percentage, measured through methods like skinfold calipers or bioelectrical impedance, gives a more direct picture of how much of your weight is fat versus lean mass.