FREE BMI
CALCULATOR
Calculate your Body Mass Index, healthy weight range, BMI Prime, and Ponderal Index instantly.
| Classification | BMI (kg/m²) | Health Risk |
|---|---|---|
| Severe Thinness | <16 | Very High |
| Moderate Thinness | 16–17 | High |
| Mild Thinness | 17–18.5 | Moderate |
| Normal Weight | 18.5–25 | Low |
| Overweight | 25–30 | Elevated |
| Obese Class I | 30–35 | High |
| Obese Class II | 35–40 | Very High |
| Obese Class III | >40 | Extremely High |
What Is BMI?
Body Mass Index measures leanness or corpulence from height and weight. A WHO-endorsed population screening tool for weight-related health risks.
BMI Prime
Ratio of your BMI to the normal upper boundary (25). A value of 1.0 = exactly at the upper edge of normal weight. Below 0.74 = underweight.
Ponderal Index
Uses height cubed instead of squared. More accurate for very tall or short individuals. Healthy range: approximately 11–14 kg/m³.
BMI Limitations
Does not distinguish muscle from fat. Does not capture fat distribution. May misclassify athletes, older adults, and some ethnic groups.
What This Calculator Does
The BMI Calculator uses the World Health Organization's Body Mass Index formula to assess weight status. Enter your height and weight to get your BMI, healthy weight range, BMI Prime, and Ponderal Index in seconds.
The Formula Explained
BMI = weight (kg) ÷ height² (m). In US units: BMI = (weight lbs × 703) ÷ height² (inches). Example: 5ft 9in (175cm), 160lbs (72kg) → BMI = 72 ÷ (1.75²) = 23.5 — Normal Weight.
What Your Result Means
A BMI under 18.5 is underweight. 18.5–24.9 is healthy. 25–29.9 is overweight. 30+ is obese. Important: BMI cannot distinguish muscle from fat — athletes often score 'overweight' despite low body fat. Always pair BMI with body fat percentage for a complete picture.
Body Fat Calculator for composition accuracy · Calorie Calculator to set your intake target
What Is BMI?
Body Mass Index (BMI) is a value derived from your weight and height — calculated as weight in kilograms divided by height in metres squared (kg/m²). Developed in the 1830s and adopted globally by the WHO and CDC, it is the most widely used screening tool for categorising weight status and estimating weight-related health risk.
BMI is best understood as a population-level screening tool, not an individual diagnosis. It identifies people who may benefit from further evaluation — but it is not a definitive measure of health, fitness, or body composition.
BMI Chart by Age
Standard WHO BMI categories apply to adults over 20 regardless of age. However, the relationship between BMI and health risk shifts with age: adults over 65 may have better outcomes at BMI 25–27 due to muscle reserve protection. Children use BMI-for-age percentile charts (CDC growth charts) rather than absolute values.
| Category | BMI (kg/m²) | WHO Classification |
|---|---|---|
| Underweight | <18.5 | Underweight |
| Normal | 18.5–24.9 | Normal weight |
| Overweight | 25.0–29.9 | Pre-obese |
| Obese Class I | 30.0–34.9 | Obese class I |
| Obese Class II | 35.0–39.9 | Obese class II |
| Obese Class III | ≥40.0 | Obese class III |
BMI for Men vs Women
The same BMI formula and thresholds apply to both sexes, but women naturally carry 8–12 percentage points more body fat than men at equivalent BMI values due to hormonal and physiological differences. Men tend to accumulate more visceral fat at the same BMI, carrying a different metabolic risk profile. Waist circumference (>102cm men, >88cm women) is a critical supplementary metric regardless of BMI.
How to Lower Your BMI
Reducing BMI requires reducing body weight through a sustained caloric deficit. A deficit of 500 calories/day below your TDEE produces roughly 0.5kg of weight loss per week. Combine this with resistance training to preserve muscle, prioritise 7–9 hours of sleep, manage stress, and target 1.6–2.4g protein per kg bodyweight. Use our Calorie Calculator and Protein Calculator for personalised targets.
BMI for Athletes
BMI is actively misleading for athletes and highly muscular individuals. Muscle is denser than fat — a professional athlete with very low body fat may register as "obese" by BMI. For athletes, body fat percentage and FFMI are far more meaningful metrics. Studies show BMI misclassifies body composition in over 54% of individuals compared against DEXA scan measurements.
Asian BMI Thresholds
WHO published separate action points for Asian populations, where metabolic risk increases at lower thresholds: overweight at BMI ≥23.0 and obese at ≥27.5. If you are of Asian descent, apply these more conservative thresholds in your assessment.