About this tool
BMI (Body Mass Index) is a screening number calculated from your height and weight. It is used by health professionals worldwide to categorize weight status and flag potential health risks. The formula is: BMI = weight (kg) ÷ height² (m²). For example, a person who is 175 cm tall and weighs 70 kg has a BMI of 22.9 — in the healthy range.
This calculator goes beyond basic BMI. It provides: (1) WHO classification (Underweight < 18.5, Healthy 18.5–24.9, Overweight 25–29.9, Obese ≥ 30); (2) Ponderal Index (a more accurate measure for tall/short individuals); (3) Body Surface Area (BSA) using the Mosteller formula; (4) Ideal weight range for your height; (5) For children ages 2–19, CDC percentile charts with age- and sex-adjusted categories. All calculations use metric or imperial units seamlessly.
Important: BMI is a screening tool, not a diagnostic. Athletes with high muscle mass may have elevated BMI despite low body fat. Always consult a healthcare professional for personalized health assessment. This tool is 100% client-side — your data never leaves your browser.
Practical Usage Examples
Calculate BMI in metric units
Person weighing 70 kg with height 175 cm wants to know their BMI.
Weight: 70 kg
Height: 175 cm
Result: BMI 22.9 (Normal weight)
Healthy range: 18.5 - 24.9Calculate BMI in imperial units
Person weighing 154 lbs with height 5'7" checks BMI status.
Weight: 154 lbs
Height: 5.58 ft (67 inches)
Result: BMI 24.1 (Normal weight)Track weight loss progress
Monitor BMI changes during a fitness journey from 85 kg to 75 kg at 170 cm height.
Before: 85 kg, 170 cm = BMI 29.4 (Overweight)
After: 75 kg, 170 cm = BMI 26.0 (Overweight approaching normal)Step-by-Step Instructions
Choose your preferred unit system: Metric (kg and cm) or Imperial (lb and inches).
Enter your height and weight in the fields provided.
For children, also select the biological sex and enter the exact age in years.
Click "Calculate BMI" to see your result instantly.
Review your BMI score, WHO category, Ponderal Index, and Body Surface Area in the results panel.
Use the ideal weight range shown to understand what weight would place you in the healthy BMI band.
Core Benefits
Supports both adults and children with age- and sex-adjusted percentile calculations for ages 2–19.
Works in metric (kg/cm) and imperial (lb/in) without any unit conversion needed.
Shows WHO BMI category, Ponderal Index, Body Surface Area, and ideal weight range in one result.
100% client-side processing — your height and weight data never leave your device.
Free and instant with no sign-up, no ads blocking results, and no download required.
Frequently Asked Questions
The WHO defines a healthy BMI range for adults as 18.5 to 24.9. Below 18.5 is underweight, 25–29.9 is overweight, and 30 or above is obese. These thresholds apply to adults of all ages, but should be interpreted alongside other health markers like waist circumference and blood pressure.
BMI is calculated by dividing your weight in kilograms by the square of your height in metres: BMI = kg ÷ m². For example, 70 kg at 1.75 m gives a BMI of 70 ÷ (1.75 × 1.75) = 22.9. In imperial units: BMI = (weight in pounds × 703) ÷ (height in inches)².
BMI does not distinguish between muscle and fat. Athletes and muscular individuals may have a high BMI despite low body fat. For these cases, the Ponderal Index and Body Surface Area provided by this tool offer additional context. Always consult a healthcare professional for a complete assessment.
The Ponderal Index (PI) is calculated as weight (kg) ÷ height³ (m³). It is more accurate than BMI for very tall or very short individuals because it accounts for three-dimensional body scaling rather than two-dimensional.
Yes. All calculations run entirely in your browser. Your height, weight, and personal data are never sent to any server.