BMI Calculator: Calculate Your Body Mass Index Online
Use our BMI calculator to quickly estimate your weight status using height and weight. Learn the BMI formula (metric & imperial), see BMI categories, understand limitations, and get practical tips, backed by WHO/CDC/NHS/ICMR references.
BMI Scale
Reviewed by Amit
Senior Developer & Calculator Specialist
What is BMI?
Body Mass Index (BMI) is a simple ratio of your weight to your height that estimates whether your weight falls in a range generally considered underweight, healthy weight, overweight, or obesity for adults. It's widely used in public health as a screening measure, not a diagnosis of body fatness or health.
However, BMI does not directly measure body fat, muscle, or fat distribution, so it can misclassify people. Athletes with high lean mass may appear overweight; older adults with less muscle may seem healthy despite higher fat; and population differences can shift risk at the same BMI. Pregnancy, edema, and illness can also distort readings.
Treat BMI as a starting point, not a diagnosis. For a fuller view, pair your BMI with waist circumference, medical history, blood pressure, and lab markers. If results raise concerns, or don't match how you feel, consult a clinician and focus on sustainable habits: balanced nutrition, regular activity with strength training, adequate sleep, and stress management.
The BMI Formula
BMI = weight (kg) ÷ [height (m)]²
Example: 70 kg and 1.75 m → 70 ÷ (1.75²) = 22.9
BMI = 703 × weight (lb) ÷ [height (in)]²
Example: 165 lb and 5′9″ (69 in) → 703 × 165 ÷ (69²) ≈ 24.3
These formulas are the standard adult BMI calculations used by major health authorities.
How to Use This BMI Calculator
1. Choose units (metric or imperial).
2. Enter your height and weight accurately (measure barefoot, recent weight).
3. Click Calculate to see your BMI value and category.
4. Review the BMI category table below to interpret your result.
5. Consider context (see Limitations of BMI) and, if unsure, discuss your result with a qualified clinician.
6. Some services also recommend checking waist circumference to better understand central fat distribution.
BMI Categories Table
| Category | BMI (kg/m²) |
|---|---|
| Underweight | < 18.5 |
| Healthy weight | 18.5 – 24.9 |
| Overweight | 25.0 – 29.9 |
| Obesity (Class I) | 30.0 – 34.9 |
| Obesity (Class II) | 35.0 – 39.9 |
| Obesity (Class III, "severe") | ≥ 40.0 |
These adult categories are used by the CDC/WHO. Note: Some Asian populations and Indian guidelines use lower BMI cut-offs (e.g., overweight ≥ 23, obesity ≥ 25) to reflect higher metabolic risk at lower BMI, check regional guidance.
Important Limitations of BMI
BMI is a useful population-level screen, but it doesn't directly measure body fat or health. Keep these caveats in mind:
- • Athletes & very muscular people: Higher BMI may reflect lean mass, not excess fat.
- • Older adults: Age-related muscle loss can inflate risk even at "normal" BMI.
- • Different body compositions: Distribution of fat (e.g., visceral vs subcutaneous) and waist size matter.
- • Pregnancy & postpartum: BMI classifications don't apply during pregnancy.
- • Fluid shifts (e.g., edema): Temporary water retention can distort BMI.
- • Children & teens: Use age- and sex-specific BMI percentiles, not adult cut-offs.
BMI Is a Screening Tool, Not a Diagnosis
A BMI result does not diagnose health, body fatness, or fitness. It is a starting point for conversations about lifestyle, metabolic risk, and whether additional assessments (e.g., waist measurement, blood pressure, labs, or body composition methods) are warranted.
Not medical advice: This page provides general information only. It does not replace personalized guidance from a licensed healthcare professional.
When to Talk to a Healthcare Professional
Consider a professional review if:
- • Your BMI is outside the healthy range and you're unsure what to change.
- • You have other risk factors (family history, high blood pressure, high blood sugar, abnormal lipids).
- • You're pregnant, breastfeeding, or managing a medical condition that affects weight or fluid balance.
- • You're a young person (under 20) - use percentiles and clinical guidance instead of adult categories.
Practical Lifestyle Tips for a Healthy Weight
Build meals around vegetables, fruits, pulses/beans, whole grains, and lean proteins; limit ultra-processed foods and sugary drinks.
Move regularly: Aim for consistent weekly activity and include strength training to preserve muscle.
Prioritize sufficient sleep and stress management; both affect appetite and metabolism.
Track gently: Periodically re-check BMI/waist and focus on sustainable habits over rapid changes.
(Follow your local health authority's recommendations and any individualized advice from your clinician.)
FAQ - BMI Calculator (What People Ask)
BMI (Body Mass Index) is a quick way to screen adult weight status using height and weight. It helps estimate population health risk but doesn't measure body fat directly.
Typically 18.5–24.9 is considered a healthy weight; ≥ 25 is overweight and ≥ 30 is obesity. Some Asian/Indian guidelines use lower thresholds (≥ 23 for overweight; ≥ 25 for obesity).
Adult BMI cut-offs are the same for men and women, but body fat distribution often differs, which is why waist measures and clinical context also matter.
BMI can overestimate body fat in muscular individuals because it doesn't distinguish muscle from fat. Consider waist size or body composition testing.
For most adults, checking periodically (e.g., when health status or habits change) is enough. Focus on long-term trends rather than single readings.
Overweight: 25.0–29.9; Obesity: ≥ 30 (with classes I, II, III). See the full table above.
Use BMI-for-age percentiles, not adult cut-offs. A child's category depends on age and sex growth charts.
BMI = 703 × lb ÷ in². (Metric is kg ÷ m².)
Yes. Fat distribution (e.g., high waist circumference), fitness level, and metabolic markers also influence risk, so BMI should be interpreted with other measures.
Combine sustainable nutrition, regular activity including resistance training, adequate sleep, and supportive habits. Seek tailored advice if you have medical conditions or take medications.
References
- • CDC — About Body Mass Index (BMI); Adult BMI Categories; BMI main page (screening tool). CDC+2CDC+2
- • WHO — BMI classification overview. WHO Apps
- • NHS — Calculate your BMI (adults); guidance on waist measurement. nhs.uk
- • ICMR / India context — Dietary Guidelines for Indians 2024 (notes WHO-Asian cut-offs); review of Indian BMI cut-offs. nin.res.inPMC