BMI Calculator — Metric & Imperial, with Category Scale
Body Mass Index (BMI) is a simple measure that uses your weight and height to estimate whether you are underweight, normal weight, overweight, or obese. Our free BMI calculator supports both metric (kg/cm) and imperial (lbs/feet-inches) units. Enter your measurements and instantly see your BMI value, category, and where you fall on the BMI scale. Important: BMI is a screening tool, not a diagnostic measure — consult a healthcare professional for a complete health assessment.
It is worth being clear about what the number is and is not. BMI was designed in the 19th century to describe populations, not individuals, and it takes no account of muscle mass, bone density, body composition, or where fat is carried. A rugby player and a sedentary person of the same height and weight get the same BMI and are in very different health situations. Used as a rough screening figure alongside waist measurement and how you actually feel, it is useful; used alone as a verdict, it is not.
How to use BMI Calculator
- Select Metric (kg/cm) or Imperial (lbs/ft-in) units.
- Enter your weight and height.
- Your BMI is calculated instantly with your category shown.
- See the visual BMI scale and your healthy weight range.
Features
- Metric and imperial units — Switch between kg/cm and lbs/ft-in instantly.
- Visual BMI scale — Color-coded scale showing Underweight, Normal, Overweight, and Obese ranges.
- Healthy weight range — Shows the ideal weight range for your height.
- Real-time calculation — Results update as you type.
- Children and teens — Add an age from 2 to 19 and the sex to get the CDC BMI-for-age percentile and the healthy weight range for that age.
- Educational breakdown — WHO BMI category definitions explained.
- 100% private — Your health data never leaves your browser.
Frequently Asked Questions
How is BMI calculated?
BMI is calculated by dividing your weight in kilograms by your height in meters squared (BMI = kg / m²). For imperial units, the formula is: BMI = (weight in pounds × 703) / (height in inches)². Our calculator handles both automatically.
What is a healthy BMI range?
According to the WHO, a BMI between 18.5 and 24.9 is considered normal weight. Below 18.5 is underweight, 25.0–29.9 is overweight, and 30.0 or above is obese. These ranges apply to adults and may vary by age and ethnicity.
Is BMI accurate for athletes?
BMI does not distinguish between muscle and fat. Athletes with high muscle mass may have an elevated BMI despite having low body fat. For a more accurate assessment, consider body fat percentage measurements or consult a healthcare provider.
What does BMI actually miss?
Body composition and fat distribution, both of which matter more than total weight. BMI cannot tell muscle from fat, so trained athletes often read as overweight. It also ignores where fat is carried, and abdominal fat carries considerably more metabolic risk than the same amount on hips and thighs. Waist-to-height ratio captures that and BMI does not.
Does BMI work the same for everyone?
No. The standard thresholds were derived largely from European populations, and health bodies apply lower cut-offs for people of South and East Asian descent, where metabolic risk appears at a lower BMI. It is also not applicable to children, who are assessed on age-and-sex percentile charts, or to pregnant people.