What formulas are used to calculate Body Mass Index?

Metric calculation uses: BMI = weight (kg) / (height (m))². Imperial calculation uses: BMI = (weight (lbs) / (height (inches))²) * 703, where 703 normalizes pounds and inches to metric SI equivalents.

What are the World Health Organization adult BMI categories?

WHO adult thresholds define: below 18.5 as underweight, 18.5 to 24.9 as normal weight, 25.0 to 29.9 as overweight, and 30.0 or higher as obese.

Does BMI account for muscle mass or bone density?

No. BMI measures total body mass relative to height. It does not differentiate between fat mass, muscular hypertrophy, bone density, or water retention.

Is my personal biometric data saved or uploaded?

No. All computations occur in browser memory. No height, weight, or health indicators are transmitted across external networks.

Free & Private Online Browser Utility

BMI Calculator

Compute Body Mass Index (BMI) and healthy weight ranges directly in your browser. This tool implements standard World Health Organization (WHO) adult screening formulas for both metric (centimeters and kilograms) and imperial (inches and pounds) systems. In metric mode, BMI equals weight in kilograms divided by height in meters squared. In imperial mode, weight in pounds is divided by height in inches squared and multiplied by the 703 conversion factor. The calculator outputs your numerical score, maps it to standard WHO adult categories (underweight, normal weight, overweight, obese), and determines the healthy weight boundary for your stature. BMI is an introductory population screening metric and does not distinguish between adipose fat tissue and lean skeletal muscle mass. All calculations execute locally on your device with complete privacy.

How to use

Step 1: Choose Measurement Units

Select either the metric system (centimeters and kilograms) or imperial system (inches and pounds).
Step 2: Enter Stature and Mass

Type your height and weight measurements into the input fields.
Step 3: Review Health Classifications

Inspect your computed BMI score, WHO classification tier, and healthy target weight range.

Options explained

Metric System Mode

Calculates BMI using height in centimeters and mass in kilograms based on the direct SI formula.

When to use: Use when working with standard international medical records or metric scales.

Imperial System Mode

Calculates BMI using inches and pounds, applying the 703 conversion factor to align with metric units.

When to use: Use when measurements are recorded in US customary pounds and inches.

Healthy Weight Boundary

Computes minimum and maximum body weights corresponding to normal BMI values of 18.5 and 24.9.

When to use: Use to identify target body mass ranges recommended for your specific height.

Worked example

Input: Height: 175 cm, Weight: 70 kg (metric mode)

Output: BMI: 22.9 (Normal weight category, healthy range: 56.7 to 76.3 kg)

Example calculation; screening result applies to non-pregnant adults aged 20 and older.

Tips & limits

BMI thresholds are standardized for adult men and women aged 20 and older; pediatric charts use percentiles.
Athletes with high muscle density may score in the overweight category despite low body fat levels.
Health evaluations should combine BMI with waist circumference and metabolic biomarkers.

Common problems

Input shows NaN or empty output: Ensure height and weight values are positive numerical entries greater than zero.
Score appears unusually high: Verify that height is entered in centimeters rather than meters when using metric mode.

Frequently Asked Questions (FAQ)

What formulas are used to calculate Body Mass Index?: Metric calculation uses: BMI = weight (kg) / (height (m))². Imperial calculation uses: BMI = (weight (lbs) / (height (inches))²) * 703, where 703 normalizes pounds and inches to metric SI equivalents.
What are the World Health Organization adult BMI categories?: WHO adult thresholds define: below 18.5 as underweight, 18.5 to 24.9 as normal weight, 25.0 to 29.9 as overweight, and 30.0 or higher as obese.
Does BMI account for muscle mass or bone density?: No. BMI measures total body mass relative to height. It does not differentiate between fat mass, muscular hypertrophy, bone density, or water retention.
Is my personal biometric data saved or uploaded?: No. All computations occur in browser memory. No height, weight, or health indicators are transmitted across external networks.