Enter weight in kilograms
Enter height in meters (e.g., 1.75)
What BMI means
Body Mass Index relates weight to height. It is widely used as a first-step screen for weight-related health risks but does not measure body fat directly. High or low values may warrant further assessment with a healthcare provider.
Adult BMI categories (WHO/CDC)
| Category | BMI range (kg/m²) |
|---|---|
| Underweight | Below 18.5 |
| Normal weight | 18.5 – 24.9 |
| Overweight | 25.0 – 29.9 |
| Obesity class I | 30.0 – 34.9 |
| Obesity class II | 35.0 – 39.9 |
| Obesity class III (severe) | 40.0 and above |
Read our BMI calculator guide for a longer explanation. Sources: WHO · CDC
What is Body Mass Index (BMI)?
Body Mass Index relates body weight to height. It is widely used as a first-step screening tool for weight categories in adults, but it does not measure body fat directly.
WHO and CDC publish adult cutoffs (underweight, normal, overweight, obese) for people aged 20 and older. Pediatric BMI requires age- and sex-specific percentiles—not the adult cutoffs in this tool.
Formula
Metric: BMI = weight (kg) ÷ height (m)²
Imperial: BMI = weight (lb) ÷ height (in)² × 703
How the calculation works
- Enter height and weight in metric or imperial units.
- Convert to consistent units if needed.
- Apply the BMI formula.
- Map the result to WHO/CDC adult categories.
Worked examples
Metric example
- Weight: 70 kg
- Height: 1.75 m
- BMI = 70 ÷ (1.75)² = 22.9
Falls in the normal adult range (18.5–24.9).
Imperial example
- Weight: 180 lb
- Height: 70 in (5 ft 10 in)
- BMI = 180 ÷ 70² × 703 ≈ 25.8
Falls in the overweight range (25.0–29.9). Athletes with high muscle mass may also score high.
Practical uses
- •Initial screening before a clinical visit
- •Tracking weight trends over time
- •Workplace wellness programs (with provider follow-up)
Limitations
- !Cannot distinguish muscle from fat
- !Not validated for children using adult cutoffs
- !Does not diagnose disease—screening only
References
Read our in-depth guide for more detail.
How This Calculator Works
Enter height and weight
Choose metric or imperial units and fill in both fields.
Apply the BMI formula
Weight is divided by height squared (× 703 for imperial).
See your category
Your number is mapped to standard adult underweight, normal, overweight, or obese ranges.
What is BMI Calculator?
BMI, or Body Mass Index, is a screening number equal to weight divided by height squared: kilograms per square metre, or pounds per square inch multiplied by 703. It sorts adults into broad weight categories but does not measure body fat directly or diagnose any condition.
Enter height and weight to compute BMI and see a standard adult category. Calculations run in your browser—nothing is stored on our servers. For children, athletes, older adults, or clinical decisions, interpret results with a qualified provider.
Screening only
BMI flags possible risk—it does not diagnose disease on its own.
Muscle vs fat
Very muscular people may score high despite low body fat.
Adults 20+
Pediatric BMI uses age- and sex-specific percentiles, not these cutoffs.
Last updated: · Published:
How to Use This Tool
Choose units
Select metric (kg, m) or imperial (lb, in).
Enter weight
Input your current weight in the selected unit system.
Enter height
Input your height in meters or inches.
Calculate
View your BMI value and WHO/CDC category instantly.
Discuss with a provider
Use the result as a starting point for health conversations, not as a diagnosis.
Pro Tips
- BMI is for adults 20+; use pediatric charts for children
- Athletes may have high BMI from muscle—consider body composition if relevant
- Waist circumference can help assess abdominal fat when BMI is borderline
- Track trends over time rather than reacting to a single reading
- Consult a healthcare provider for personalized advice