WHO BMI Classification for adults
| Classification | BMI Range | Health risk |
|---|---|---|
| Underweight | < 18.5 | Increased |
| Normal weight | 18.5 - 24.9 | Low |
| Overweight | 25.0 - 29.9 | Increased |
| Obese | ≥ 30.0 | High |
BMI CALCULATOR
Calculate your BMI with age and gender adjustments. Get BMR, body fat %, and ideal weight range.
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AVG BMI
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How to calculate your BMI
Calculate Body Mass Index from height and weight in 3 steps
Full Documentation DocsEnter data
Input weight, height, age, and gender
Instant results
Get BMI with visual scale indicator
Health insights
View BMR, body fat %, and ideal weight
Your data stays in browser
Metric & Imperial units
BMR & TDEE calculator
Age-adjusted BMI ranges
Why choose this BMI calculator?
Age-adjusted Body Mass Index tool with BMR, TDEE, and body fat percentage
Instant calculation
Get your BMI result immediately with visual indicators and health category classification.
Age-adjusted BMI
Children under 18, standard WHO for adults, and adjusted ranges for seniors over 65.
Metric and imperial units
Supports both metric (kg/cm) and imperial (lbs/ft,in) measurement systems with instant conversion.
BMR and TDEE calculator
Mifflin-St Jeor BMR formula with 5 activity levels for TDEE. Includes daily calorie targets for weight loss and gain.
Ideal weight for your height
Calculates your healthy weight range based on BMI 18.5-24.9. Shows exactly how many kg or lbs to gain or lose.
Achievement badges
Unlock 10 badges by tracking progress, maintaining streaks, and reaching health milestones.
Frequently Asked Questions
Everything you need to know about BMI
What is BMI?
BMI (Body Mass Index) is a numerical value calculated by dividing weight in kilograms by height in meters squared (kg/m²). Developed by Adolphe Quetelet in the 1830s, it is now the standard screening metric adopted by the WHO to classify underweight, normal weight, overweight, and obesity in adults.
What is a healthy BMI range?
A healthy BMI range for adults is 18.5-24.9 according to WHO standards. Below 18.5 is underweight, 25-29.9 is overweight, and 30+ is obese. This calculator also uses age-adjusted thresholds for children under 18 and seniors over 65.
Is BMI accurate for athletes and muscular people?
BMI does not distinguish between muscle and fat mass, so athletes with high muscle mass may be classified as overweight despite low body fat. This calculator includes a Jackson-Pollock body fat percentage estimate as a complementary metric for a more complete picture.
How do I calculate BMI manually?
For metric: BMI = weight(kg) / height(m)². For imperial: BMI = (weight(lbs) x 703) / height(inches)². For example, a person weighing 70 kg at 175 cm tall has a BMI of 70 / 1.75² = 22.9.
Is BMI different for men and women?
The BMI formula is identical for men and women, but body fat distribution differs. At the same BMI, women typically carry 5-10% more body fat than men. This calculator uses the Jackson-Pollock formula with separate coefficients for each gender.
Can children and seniors use this BMI calculator?
Yes. This calculator uses age-adjusted BMI thresholds: children under 18 use modified cutoffs (15/23/28), seniors over 65 use higher thresholds (20/27/32) to account for natural changes in body composition with age.
How much should I weigh for my height?
Your ideal weight range is calculated by multiplying your height in meters squared by BMI 18.5-24.9. For example, at 170 cm, the healthy range is 53.5-72.0 kg. This calculator shows your exact range and how many kg or lbs to gain or lose.
What are BMR and TDEE?
BMR (Basal Metabolic Rate) is the number of calories your body burns at rest, calculated here using the Mifflin-St Jeor formula. TDEE (Total Daily Energy Expenditure) multiplies BMR by your activity level (1.2-1.9) to estimate total daily calorie needs.
Technical Details
How this BMI calculator computes body mass index, BMR, and body fat percentage
BMI Formula
This BMI calculator implements the standard body mass index formula for both metric and imperial units: BMI = weight(kg) / height(m)^2 or BMI = (weight(lbs) x 703) / height(inches)^2. Results are rounded to one decimal place and classified into WHO categories: underweight (below 18.5), normal (18.5-24.9), overweight (25-29.9), and obese (30+).
WHO Health Categories
This calculator uses age-adjusted BMI thresholds beyond the standard WHO ranges. Children under 18 use modified cutoffs (15/23/28), adults follow standard WHO classification, and seniors over 65 use higher thresholds (20/27/32) that account for natural body composition changes with aging. Each category includes a color-coded visual scale indicator.
Unit Conversion
The body mass index calculator supports both metric (kg/cm) and imperial (lbs/ft-in) measurement systems with instant conversion between them. Height accepts centimeters or feet/inches input, weight accepts kilograms or pounds. All conversions use IEEE 754 double-precision floating-point arithmetic for accuracy.
Analytics and Storage
Calculation history and usage statistics persist in IndexedDB across browser sessions. The BMI calculator tracks total calculations, average BMI values, and most common categories. A sticky calculator widget follows as you scroll for quick recalculations. All processing runs client-side with zero server communication.
Body Fat and BMR Calculation
Body fat percentage is estimated using the Jackson-Pollock formula with separate coefficients for men (1.20 x BMI + 0.23 x age - 16.2) and women (1.20 x BMI + 0.23 x age - 5.4). BMR uses the Mifflin-St Jeor equation, and TDEE is calculated by multiplying BMR by one of 5 activity levels ranging from sedentary (1.2) to extra active (1.9).
Goal Tracking and PDF Export
Set a target weight and track progress with calculated daily calorie adjustments of plus or minus 500 kcal from your TDEE. Generate a PDF report with your complete BMI analysis, health metrics, and recommendations. Share results via URL parameters that encode your measurements for easy comparison across sessions.