BMI Calculator
Online BMI calculator with metric and US units
Calculate Your BMI
How BMI is calculated
BMI (Body Mass Index) compares weight to height squared. It is a screening tool, not a diagnosis of body fat or health.
Metric: height in meters h, weight in kilograms w.
BMI = w ÷ h² (units: kg/m²)
Example: 70 kg and 1.70 m → BMI = 70 ÷ (1.70 × 1.70) ≈ 24.2.
US customary: total height in inches H, weight in pounds W. The factor 703 converts lb/in² to the same kg/m² scale.
BMI = (W × 703) ÷ H²
This matches what this calculator uses when you choose US Units (feet and inches are combined into total inches before squaring).
Adult categories (this calculator)
Cutoffs follow common WHO / CDC-style ranges for adults. Weight limits for each category depend on your height—same BMI always means the same ratio of weight to height², not the same weight for everyone.
If height is h meters: weight (kg) = BMI × h². In US units: weight (lbs) = (BMI × H²) ÷ 703. At 170 cm (1.70 m), the "normal" band is roughly 53.5–72.0 kg; at 5 ft 10 in (70 in), roughly 129–174 lbs for BMI 18.5–24.9.
| Category | BMI range | Weight vs height (summary) | Description |
|---|---|---|---|
| Underweight | < 18.5 | Below 18.5 × h² (kg) or (18.5 × H²) ÷ 703 (lbs) | May indicate low body weight for height. Discuss with a clinician if unintended or concerning. |
| Normal weight | 18.5 – 24.9 | Between lower and upper bound using 18.5 and 24.9 with your h or H | Associated with the broad "healthy weight" range for many adults; still only one screening measure. |
| Overweight | 25.0 – 29.9 | From 25 × h² up to just under 30 × h² (same idea in lbs with H) | Higher weight for height; may warrant lifestyle discussion or further assessment—not a judgment of health by itself. |
| Obese | 30.0 – 34.9 | Often called class I obesity in clinical charts | Substantially elevated BMI; risk factors vary by person; professional guidance is often recommended. |
| Severely obese | ≥ 35 | Class II/III obesity in many systems (e.g. 35–39.9, ≥ 40) | This tool groups all BMI ≥ 35 here; finer classes exist in medical references. |
Good to know
- BMI does not distinguish muscle from fat; very muscular people can have a high BMI without high body fat.
- It may be less informative for some older adults, children (use age-specific percentiles), and during pregnancy.
- Ethnicity and other factors sometimes lead guidelines to use different cutoffs (e.g. for diabetes risk)—this page uses the standard adult ranges above.
- Waist circumference, diet, activity, blood pressure, and lab values add context that BMI alone cannot provide.
BMI Calculator Guide
1. How can I calculate BMI and read weight categories on this page?
- Select Metric (kg/cm) or US Units (lbs/ft, in).
- Enter your height and weight in the appropriate fields.
- Click Calculate BMI to see your result and health category.
2. How does this BMI calculator use height and weight in metric or imperial units?
BMI = Weight ÷ Height². Metric: kg/(m²). US: (Weight lbs × 703) ÷ Height in².
Categories: Underweight (<18.5), Normal (18.5–24.9), Overweight (25–29.9), Obese (30–34.9), Severely obese (≥35). See the reference table below the calculator for details.
3. What is BMI, and what are its limits for judging health?
Free online BMI calculator for health assessment. Calculate your Body Mass Index with metric or imperial units. Results include health category classification.
Note: BMI does not reflect body composition, skeletal structure, age, or other individual factors.
4. Why check BMI with a private in-browser calculator?
- Dual unit support: Metric and US units.
- Visual scale showing your position.
- Health category with recommendations.
- All calculations run locally in your browser.
5. When is BMI screening used alongside other health information?
- Health screening and body composition assessment.
- Fitness goals and weight management.
- Research, studies, and population health.
- Personal health monitoring.