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Calculate Your Body Mass Index • Get Smart Health Insights
Get comprehensive body composition analysis with BMI, body fat %, waist-to-hip ratio, and personalized health insights
📊
Underweight
<18.5
✅
Normal
18.5-24.9
⚠️
Overweight
25-29.9
🚨
Obese
≥30
Your BMI Score
Precise BMI using the standard formula
Health Category
Underweight, Normal, Overweight, or Obese classification
Ideal Weight Range
The healthy weight range for your exact height
Health Risk Assessment
What your BMI means for long-term health
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Results in milliseconds
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Enter Height & Weight
Use imperial (lbs/ft) or metric (kg/cm)
Get Your BMI
Instant score with health category and risk level
See Your Healthy Range
The target weight range for your height
Body Mass Index (BMI) is a simple numerical measure of a person's body weight relative to their height. It was developed by Belgian mathematician Adolphe Quetelet in the 1830s and has since been adopted by the World Health Organization and CDC as a standard screening tool for weight-related health risks. While imperfect, it provides a quick, cost-free method for identifying potential weight problems.
BMI Formula
Metric: BMI = weight (kg) ÷ height (m)²
Imperial: BMI = 703 × weight (lbs) ÷ height (in)²
Under 18.5
Underweight
18.5 – 24.9
Normal weight
25.0 – 29.9
Overweight
30.0+
Obese
Height: 5'10" (70 inches) | Weight: 180 lbs
BMI = 703 × 180 ÷ (70)² = 126,540 ÷ 4,900 = 25.8 — Overweight. To reach a normal BMI (under 25), this person would need to weigh approximately 174 lbs or less.
According to the World Health Organization and CDC, BMI categories for adults are: Under 18.5 = Underweight; 18.5–24.9 = Normal (healthy) weight; 25.0–29.9 = Overweight; 30.0–34.9 = Obese Class I; 35.0–39.9 = Obese Class II; 40.0 and above = Obese Class III (severe). A BMI between 18.5 and 24.9 is considered the healthy range for most adults.
BMI is calculated differently depending on the unit system. In metric: BMI = weight (kg) ÷ height (m)². In imperial: BMI = 703 × weight (lbs) ÷ height (inches)². Example: a person who is 5'10" (70 inches) and weighs 180 lbs has a BMI of 703 × 180 ÷ 70² = 703 × 180 ÷ 4,900 = 25.8, which falls in the Overweight category.
BMI is a useful screening tool but has important limitations. It does not distinguish between muscle mass and fat mass, does not account for age, sex, ethnicity, or body fat distribution. A muscular athlete may have a high BMI but very low body fat. Older adults may have a normal BMI but carry more fat relative to muscle. BMI should be considered alongside other measures like waist circumference, body fat percentage, blood pressure, and blood work.
Yes. BMI cannot distinguish muscle from fat. Highly muscular athletes and bodybuilders often fall in the "overweight" or "obese" BMI category despite having very low body fat percentages and excellent health markers. For muscular individuals, body fat percentage (measured via DEXA scan, hydrostatic weighing, or the Navy method) is a more accurate health indicator than BMI.
The US Navy body fat formula uses circumference measurements to estimate body fat percentage. For men: % body fat = 86.010 × log10(abdomen – neck) – 70.041 × log10(height) + 36.76. For women: % body fat = 163.205 × log10(waist + hip – neck) – 97.684 × log10(height) – 78.387. This method is more accurate than BMI for assessing body composition, particularly for athletic individuals, because it specifically measures fat-carrying areas.
A BMI of 30.0 or higher is classified as obese. Obesity is further divided into three classes: Class I (BMI 30–34.9), Class II (BMI 35–39.9), and Class III or "severe obesity" (BMI 40+). Obesity is associated with increased risk of type 2 diabetes, heart disease, high blood pressure, sleep apnea, joint problems, and certain cancers. Even a 5–10% reduction in body weight can significantly reduce these risks.
BMI decreases when you lose weight, which requires a sustained calorie deficit — consuming fewer calories than you burn. The most evidence-based approach combines a moderate calorie deficit (300–500 calories/day below TDEE), strength training to preserve muscle mass, and cardiovascular exercise to increase calorie burn. Losing 1–2 pounds per week is considered safe and sustainable. Rapid weight loss often results in muscle loss, which can worsen body composition even if BMI improves.
Research suggests that slightly higher BMI may be protective for adults over 65. Some studies indicate that a BMI of 25–27 (technically "overweight" by standard classification) may be optimal for older adults in terms of longevity and muscle preservation. Being underweight (BMI under 22) in older age is associated with increased mortality risk, frailty, and poor recovery from illness. Consult your physician for age-appropriate BMI guidance.
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