BMI Calculator: Free Body Mass Index Calculator
Calculate your BMI (Body Mass Index) instantly. Free calculator with imperial and metric units to understand your health status.
Quick answer: BMI is calculated by dividing your weight by your height squared. A BMI of 18.5-24.9 is considered normal, but BMI has limitations for athletes and doesn't measure body fat directly.
What is BMI?
BMI (Body Mass Index) is a measure of body fat based on height and weight. It's used by doctors worldwide to categorize weight status and assess health risks. Over 1 billion people globally are classified as obese by BMI standards.
BMI Categories
| BMI Range | Category | Health Risk |
|---|---|---|
| Below 18.5 | Underweight | Moderate |
| 18.5 – 24.9 | Normal weight | Low |
| 25.0 – 29.9 | Overweight | Increased |
| 30.0 – 34.9 | Obese (Class I) | High |
| 35.0 – 39.9 | Obese (Class II) | Very High |
| 40.0+ | Obese (Class III) | Extremely High |
How to Calculate BMI
Metric formula: BMI = weight (kg) / height (m)²
Imperial formula: BMI = (weight (lbs) / height (inches)²) × 703
⚖️ Calculate Your BMI Now
Free BMI calculator with instant results and health recommendations.
Calculate BMI →BMI by Age and Gender
While the standard BMI chart applies to all adults equally, research suggests slightly different optimal ranges by age.
Limitations of BMI
📐 How We Calculate This
Our calculations follow clinical guidelines from the CDC, WHO, and NIH. BMI uses the standard formula: weight (kg) / height (m²). Caloric estimates use the Mifflin-St Jeor equation, validated as the most accurate resting metabolic rate formula.
These tools are for informational purposes and do not replace medical advice. Consult a healthcare provider for personalized health recommendations.
📚 Sources & References
⚠️ Important: BMI is a useful screening tool, but it has significant limitations. It doesn't measure body fat directly and doesn't account for muscle mass, bone density, or fat distribution.
- Doesn't measure body fat directly — A muscular athlete can have an "overweight" BMI with low body fat
- Doesn't account for fat distribution — Belly fat is more dangerous than hip fat, but BMI doesn't distinguish
- Age and gender blind — Same scale for everyone, despite natural differences
- Racial differences — Health risks may occur at different BMIs for different populations
How to Improve Your BMI
If Overweight (BMI 25-29.9)
- Create a modest calorie deficit of 250-500 calories/day
- Increase daily movement — aim for 10,000 steps
- Focus on protein and fiber for satiety
- Aim for 1-2 lbs of weight loss per week
If Underweight (BMI below 18.5)
- Increase calorie intake by 300-500 calories/day
- Eat nutrient-dense foods (nuts, avocados, whole grains)
- Add strength training to build muscle mass
- Consult a doctor to rule out underlying conditions
Better Metrics Than BMI
For a more complete picture of health, also check:
- Waist circumference: Men <40", Women <35" (lower diabetes/heart disease risk)
- Body fat percentage: Measured by calipers, DEXA scan, or bioelectrical impedance
- Waist-to-hip ratio: Should be <0.9 for men, <0.85 for women
Frequently Asked Questions
Is BMI accurate for everyone?
No. BMI can misclassify athletes with high muscle mass as overweight or obese. It also doesn't account for age, gender, or ethnicity differences in body composition.
What's a healthy BMI for women vs men?
The standard BMI ranges (18.5-24.9 for normal weight) apply to both men and women, though women naturally have higher body fat percentages at the same BMI.
Can I be healthy with a BMI over 25?
Yes, if the excess weight is muscle mass or if you have good metabolic health markers (normal blood pressure, cholesterol, blood sugar). However, most people with BMI over 25 have increased health risks.