What This Calculator Estimates
Body Mass Index (BMI) is a simple screening measure that divides weight by the square of height to estimate whether someone falls into an underweight, normal, overweight, or obese category, widely used by health organizations as a quick population-level screening tool rather than a precise individual diagnostic measure. Because BMI doesn't distinguish between muscle and fat mass, it can misclassify very muscular or very lean individuals, so it works best as a starting point alongside other health indicators rather than a standalone verdict.
How to Use This Calculator
- Select the height and weight units you want to use.
- Enter current height and weight values.
- Click Calculate BMI to view the estimate.
- Review the category shown with the result.
- Use the estimate as informational screening only.
Formula / Method Used
BMI = weight (kg) ÷ height (m)². In imperial units: BMI = 703 × weight (lb) ÷ height (in)². The CDC/WHO adult categories are: underweight below 18.5, healthy weight 18.5–24.9, overweight 25–29.9, and obese 30 and above.
Worked Example
A person weighing 70kg at 1.75m: BMI = 70 ÷ (1.75)² = 70 ÷ 3.0625 ≈ 22.9, which falls in the healthy-weight range.
Limitations
BMI doesn't distinguish muscle from fat, so it can misclassify very muscular people as overweight and underestimate risk in people with low muscle mass. It's a population-level screening tool, not an individual diagnostic measure.
Official Sources
Related Calculators
Tips for a More Accurate Estimate
- Use BMI as a starting screening point, not a definitive health verdict.
- Pair BMI with waist-to-hip ratio or body fat percentage for a fuller picture.
- Remember BMI categories may not apply the same way to very muscular individuals.
- Track BMI trends over time rather than fixating on a single reading.
- Discuss your specific BMI result with a healthcare provider for personalized context.
Frequently Asked Questions
What does BMI estimate?
BMI estimates body size relative to height and weight using a simple screening formula (weight divided by height squared), placing the result into standard categories like underweight, normal, overweight, or obese.
Is BMI a medical diagnosis?
No, BMI is an informational screening measure, not a medical diagnosis. Two people with the same BMI can have very different body compositions and health profiles.
Why can BMI be misleading for athletic people?
BMI doesn't distinguish between muscle and fat mass, so muscular individuals with low body fat can be classified as 'overweight' or 'obese' by BMI alone despite being fit and healthy.
What other measures complement BMI?
Waist-to-hip ratio, body fat percentage, and waist circumference are commonly used alongside BMI to get a fuller picture of body composition and health risk.
How often should I recalculate my BMI?
Recalculate whenever your weight changes meaningfully, and treat trends over time as more informative than any single BMI reading.
This calculator provides informational health estimates only and is not medical advice. Consider professional guidance for personal health decisions.
Last updated: May 11, 2026