BMI Calculator Online: Check Your Body Mass Index Instantly
Use this fast and accurate BMI Calculator to check your Body Mass Index, understand your BMI category, and find your healthy weight range instantly.
Enter your height accurately for correct BMI calculation
Use your most recent or average weight
Required for Child/Teen BMI percentile calculation
Helps provide more accurate interpretation for children
Ready to Calculate Your BMI
Enter your height and weight above to check your Body Mass Index and see where you fall on the BMI scale
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What Is BMI?
Body Mass Index (BMI) is a simple numerical measure used worldwide to estimate whether a person's weight falls within a healthy range. It provides a quick way to understand whether your weight is underweight, normal, overweight, or in the obesity range based on your height.
Although BMI does not measure body fat directly, it serves as a widely accepted screening tool used by medical professionals, researchers, and global health organizations.
How BMI Is Calculated
BMI is calculated using a person's weight and height. The formula divides body weight by the square of height. This calculation gives a value that falls into standard classification categories defined by the World Health Organization (WHO) and Centers for Disease Control and Prevention (CDC).
BMI Formula (Metric and Imperial Systems)
Metric Formula
BMI = weight (kg) ÷ height (m²)
Example: If your weight is 70 kg and your height is 1.70 m: BMI = 70 ÷ (1.70 × 1.70) = 24.22
Imperial Formula
BMI = 703 × weight (lb) ÷ height (in²)
Example: If your weight is 165 lbs and your height is 68 inches: BMI = 703 × 165 ÷ (68 × 68) ≈ 25.09
BMI Ranges Table (Adults + Children)
Adult BMI Classification (WHO Standards)
| BMI Range | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Normal Weight |
| 25.0 – 29.9 | Overweight |
| 30.0 – 34.9 | Obesity Class I |
| 35.0 – 39.9 | Obesity Class II |
| 40.0 and above | Obesity Class III |
Source: WHO Adult BMI Classification
Children & Teen BMI (Ages 2–19) – CDC Percentiles
Unlike adults, BMI for children is age- and sex-specific. The CDC uses percentiles:
| Percentile Range | Category |
|---|---|
| Below 5th percentile | Underweight |
| 5th – 85th percentile | Healthy Weight |
| 85th – 95th percentile | Overweight |
| 95th percentile and above | Obesity |
Source: CDC BMI Categories
How to Use the BMI Calculator
- 1. Select your measurement system: Choose metric (kg/cm) or imperial (lbs/ft/in).
- 2. Enter your height: Accurate height yields accurate BMI.
- 3. Enter your weight: Use your most recent or average weight.
- 4. Choose your category: Adult BMI or Child/Teen BMI.
- 5. Instantly see your BMI score, category, and healthy weight range.
Your result will also display a visual BMI chart to help you interpret your number easily.
Example BMI Calculations
Example 1: Adult Male
- Weight: 80 kg
- Height: 1.78 m
- BMI = 80 ÷ (1.78 × 1.78) = 25.22
- Category: Overweight
Example 2: Adult Female
- Weight: 62 kg
- Height: 1.60 m
- BMI = 62 ÷ (1.60 × 1.60) = 24.22
- Category: Normal Weight
Example 3: 14-Year-Old Boy (Child BMI Percentile)
- BMI Score: 23
- According to CDC growth charts, BMI = 23 for a 14-year-old boy falls in the 85th–95th percentile, which indicates Overweight.
Factors That Affect BMI Accuracy
While BMI is widely used, several factors can influence how accurate or meaningful the number is for each person.
1. Muscle Mass
Athletes or individuals with high muscle mass may have a high BMI despite low body fat.
2. Age
Older adults tend to lose muscle and gain fat, affecting BMI interpretation.
3. Ethnicity & Genetics
Asian populations often have health risks at lower BMI scores. Black populations may have higher muscle mass at the same BMI. WHO and national guidelines often adjust BMI risk thresholds for specific populations.
4. Pregnancy
BMI is not used to assess weight status during pregnancy.
5. Body Composition Variations
People with similar BMI can have very different body fat percentages.
Therefore, BMI should be viewed as a screening tool, not a diagnostic measure.
Health Risks Linked With Each BMI Category
Underweight
Potential risks include:
- Nutrient deficiencies
- Weakened immune system
- Osteoporosis
- Fertility issues
Normal Weight
Associated with:
- Lower risk of metabolic diseases
- Better cardiovascular health
- Reduced risk of diabetes
Overweight
May increase risk for:
- Hypertension
- Elevated cholesterol
- Type 2 diabetes
- Joint problems
Obesity (Class I–III)
Significantly increases risk for:
- Heart disease
- Stroke
- Type 2 diabetes
- Sleep apnea
- Fatty liver disease
- Certain cancers
BMI helps identify when someone may need lifestyle or medical interventions.
BMI Chart with Ranges
A typical BMI range chart looks like this:
This visual scale helps users understand where they fall relative to healthy ranges.
Healthy Weight Tips
1. Follow a Balanced Diet
Include lean proteins, whole grains, healthy fats, fruits, and vegetables.
2. Stay Physically Active
WHO recommends 150 minutes of moderate activity per week for adults.
3. Maintain Hydration
Water supports metabolism and appetite control.
4. Prioritize Sleep
7–9 hours per night helps regulate hormones related to hunger and weight.
5. Monitor Progress Regularly
Tracking your BMI, waist circumference, or body fat percentage can help maintain long-term health.
Limitations of BMI
People commonly search for "Is BMI flawed?" and the answer is yes, but it's still useful.
Key Limitations
- 1. Does not measure body fat directly
- 2. Cannot differentiate between muscle and fat
- 3. Does not consider fat distribution (visceral vs. subcutaneous fat)
- 4. Does not account for age-related muscle loss
- 5. Population-specific differences may require adjustments
BMI is best paired with:
- Waist-to-height ratio
- Body fat percentage
- Medical evaluations
This yields a more complete picture of health.
BMI vs Body Fat vs Waist-to-Height Ratio
1. BMI (Body Mass Index)
Pros: Simple, fast, widely accepted
Cons: Does not measure fat directly
2. Body Fat Percentage
Measured by DEXA scans, calipers, or smart scales. More accurate for understanding true fat mass.
3. Waist-to-Height Ratio (WHtR)
Formula: Waist ÷ Height
A WHtR above 0.5 may indicate higher health risks.
Useful for identifying visceral fat risks.
Which Is Best?
- BMI = best general screening tool
- Body Fat % = best measure of actual fatness
- Waist-to-Height Ratio = best for determining abdominal fat
Using all three gives the most accurate health assessment.
Medical Disclaimer
This BMI Calculator provides general information only and is not a substitute for medical advice, diagnosis, or treatment. Always consult a qualified healthcare professional for personalized health recommendations.
