BMI Calculator
Estimate adult body mass index from height and weight.
This page is an editable estimator with realistic defaults so you can model your own situation in minutes.
BMI = weight in kilograms divided by height in meters squared.
US inputs are converted before calculating.
| BMI formula | kg / m^2 | Adult BMI categories are broad screening ranges. |
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Assumptions
- BMI does not measure body fat directly.
- Adult BMI is less useful for children, pregnancy, athletes, or unusual body composition.
How this calculator works
Formula used
BMI = weight in kilograms divided by height in meters squared. US inputs are converted before calculating.
Example calculation
Plug in your own numbers and the result updates instantly. BMI = weight in kilograms divided by height in meters squared. US inputs are converted before calculating.
How this calculator estimates the result
The calculator converts U.S. units to metric when needed, then computes BMI as weight in kilograms divided by height in meters squared. The result is mapped to the World Health Organization adult BMI categories: Underweight (<18.5), Normal weight (18.5–24.9), Overweight (25.0–29.9), Obesity Class I (30.0–34.9), Class II (35.0–39.9), and Class III (≥40.0).
Assumptions baked in
- Adults age 20 and over. Children and teens use age-and-sex-specific BMI-for-age percentiles, not adult categories.
- Standing height and current body weight, clothed lightly.
- 1 inch = 2.54 cm and 1 pound = 0.45359237 kg conversions.
What this calculator does not do
- Does not measure body composition; athletes and muscular individuals can score 'overweight' while having low body fat.
- Underestimates fat mass in older adults who have lost muscle.
- Not validated for pregnant people; clinical pregnancy BMI uses pre-pregnancy weight.
- Does not account for waist circumference, ethnicity-specific cutoffs, or metabolic health markers.
A step-by-step example
Scenario: Adult, 5 feet 9 inches tall, 170 pounds.
- Height = (5 × 12 + 9) × 0.0254 = 1.7526 m.
- Weight = 170 × 0.45359237 ≈ 77.11 kg.
- BMI = 77.11 / (1.7526)^2 = 77.11 / 3.0716.
Result: BMI ≈ 25.1, which falls just inside the 'Overweight' category (25.0–29.9). A clinician would also look at waist circumference, blood pressure, lipids, and activity level before drawing any conclusion.
Official references
Sources open in a new tab. Numbers in formulas and brackets above reflect the most recent publicly available values at the time of writing and are reviewed periodically by the TDL Expert Panel.
BMI Calculator FAQ
Is this bmi calculator medical advice?
No. It is an educational estimate only and should not be used to diagnose, treat, or make medical, nutrition, legal, or emergency decisions.
Why might my real result be different?
Age, sex, body composition, pregnancy, medications, medical conditions, training status, lab methods, and measurement accuracy can all change real-world results.
Should I check these results with a professional?
Yes. Confirm health, nutrition, fitness, kidney function, alcohol, or safety decisions with a qualified professional or official source.