BMI Calculator
Calculate your Body Mass Index with a live visual gauge and personalized insights. Adjust the sliders to see your BMI update instantly — no button needed.
How to use the BMI Calculator
Enter your height and weight using the number fields or the sliders — the gauge and results update instantly as you type or drag, with no calculate button needed. Switch between metric (centimeters and kilograms) and imperial (feet, inches, and pounds) at any time; your values convert automatically.
Select an age group to see a commonly referenced BMI range for that bracket. The insights panel below the results updates automatically based on your BMI category.
How is BMI calculated?
Body Mass Index is calculated from height and weight using one of two equivalent formulas, depending on the unit system:
The result is a single number used to categorize weight status for adults, regardless of sex or frame size:
| BMI Range | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Normal weight |
| 25.0 – 29.9 | Overweight |
| 30.0 and above | Obese |
These World Health Organization cutoffs apply broadly to adults. Some wellness sources suggest slightly higher reference ranges for older adults, since body composition naturally shifts with age — the age-group note in the calculator reflects this general guidance, not a clinical assessment.
Frequently Asked Questions
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How is BMI calculated?
BMI is calculated by dividing weight in kilograms by height in meters squared: BMI = weight (kg) ÷ height (m)². In imperial units, the formula is BMI = 703 × weight (lb) ÷ height (in)².
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What are the standard BMI categories?
For adults, a BMI below 18.5 is considered underweight, 18.5 to 24.9 is normal weight, 25 to 29.9 is overweight, and 30 or above is considered obese, according to World Health Organization classifications.
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Does BMI change with age?
The standard BMI formula and category cutoffs are the same for all adults. Some wellness guidance suggests slightly higher reference ranges for older adults, since body composition tends to shift with age, but this is general guidance rather than a medical diagnosis.
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Is BMI an accurate measure of health?
BMI is a simple screening tool based only on height and weight. It doesn't distinguish between muscle and fat, and it doesn't account for frame size, sex, or where fat is distributed in the body. It's best used as a general starting point rather than a complete health assessment.
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What should I do if my BMI is outside the normal range?
A BMI outside the typical range isn't a diagnosis on its own. If you have concerns about your weight or health, it's best to discuss your individual situation with a doctor or registered dietitian, who can consider your full health picture.
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Is my data kept private?
Yes — all calculations run entirely in your browser using JavaScript. Nothing you enter is transmitted to any server or stored anywhere. See our Privacy Policy for full details.
Methodology & Limitations
This tool calculates adult BMI from height and weight: kilograms divided by metres squared. The displayed adult reference categories use World Health Organization thresholds.
Limitations: BMI is a screening measure, not a diagnosis. It does not measure body composition or account for all individual factors. It is not designed for children or adolescents; discuss health concerns with a qualified clinician.
Source: World Health Organization: Obesity and overweight.
Prepared and reviewed by MonkeyTactics. Last reviewed .