BMI Calculator
Free online BMI calculator. Calculate your Body Mass Index with metric or imperial units. Get weight category, health risk level and ideal weight range instantly.
<18.5 Normal
18.5-25 Overweight
25-30 Obese
>30
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What is BMI?
Body Mass Index (BMI) is a simple screening tool that estimates whether a person has a healthy body weight relative to their height. It's calculated by dividing weight in kilograms by the square of height in meters. Despite its simplicity, BMI is used worldwide by healthcare providers, researchers, and public health organizations as a first-line obesity screening metric.
BMI Formula & Calculation
The formula is straightforward — the same one used by the CDC and WHO:
BMI Categories (WHO & CDC Standards)
| BMI Range | Category | Health Risk |
|---|---|---|
| Below 18.5 | Underweight | Nutritional deficiency, bone loss |
| 18.5 – 24.9 | Normal Weight ✓ | Lowest risk for weight-related disease |
| 25.0 – 29.9 | Overweight | Elevated risk of metabolic syndrome |
| 30.0 – 34.9 | Obese Class I | High risk — type 2 diabetes, heart disease |
| 35.0 – 39.9 | Obese Class II | Very high risk |
| 40+ | Obese Class III (Severe) | Extremely high risk, consider medical care |
Limitations of BMI
BMI is a screening tool, not a diagnostic measure. It has well-documented limitations that are important to understand:
- Doesn't distinguish fat from muscle — A bodybuilder with high muscle mass may be classified as "obese" despite low body fat.
- Doesn't account for fat distribution — Abdominal fat is more dangerous than fat elsewhere. Waist circumference is often a better cardiovascular risk predictor.
- Age and sex differences — Older adults naturally carry more fat; women typically have more body fat than men at the same BMI.
- Ethnicity variations — Asian populations may face higher health risks at lower BMI thresholds (some guidelines suggest 23+ as overweight for Asian adults).
💡 Beyond BMI: For a fuller picture of your health, consider also tracking waist circumference (healthy: <35" women, <40" men), waist-to-hip ratio, and body fat percentage. Use our Body Fat Calculator for a complementary assessment.
⭐ Why Use BestMiniApps BMI Calculator?
Frequently Asked Questions
Is BMI accurate for athletes and muscular people?
No — BMI significantly overestimates body fat in muscular individuals. A professional athlete may have a BMI of 28 (technically "overweight") but only 10% body fat. For athletes, body fat percentage measurement (via DEXA scan, calipers, or bioelectrical impedance) is a more accurate assessment tool.
What BMI is considered healthy?
For most adults, BMI 18.5–24.9 is considered healthy by the WHO and CDC. Research suggests the lowest mortality risk is typically around BMI 22–23. Note: these ranges are for adults 20+; children and teens use age- and sex-specific BMI percentile charts instead.
How is BMI different for children?
Children's BMI is age- and sex-specific and expressed as a percentile (not a fixed number). A BMI at or above the 95th percentile for age and sex is considered obese; 85th–94th percentile is overweight. Use our BMI Percentile Calculator for Kids for pediatric assessments.
Can I lower my BMI quickly?
BMI changes as your weight changes. A safe rate of weight loss is 0.5–1 kg (1–2 lbs) per week through a combination of calorie deficit and physical activity. Losing 5–10% of body weight significantly reduces health risks even if BMI remains in the overweight range. Focus on sustainable lifestyle changes rather than rapid weight loss.