BMI Calculator: How to Calculate and Understand Your Body Mass Index for Better Health

Body Mass Index (BMI) is a simple calculation that estimates whether you have a healthy body weight for your height. While it is not a perfect measure of health (it does not distinguish fat from muscle), it remains a useful starting point for understanding weight-related health risks. Use our free BMI Calculator to find your BMI in seconds.

How to Calculate BMI

The formula is straightforward:

• Metric: BMI = weight (kg) ÷ height² (m²)
• Imperial: BMI = (weight in lb ÷ height in inches²) × 703

Example: A person who weighs 70 kg and is 1.75 m tall has a BMI of 70 ÷ (1.75 × 1.75) = 22.9 — within the normal range.

BMI Categories (WHO Standards)

Category	BMI Range	Health Risk
Underweight	Below 18.5	Increased risk of malnutrition, osteoporosis
Normal weight	18.5 – 24.9	Lowest risk for weight-related conditions
Overweight	25.0 – 29.9	Moderate risk for heart disease, diabetes
Obese Class I	30.0 – 34.9	High risk for cardiovascular issues
Obese Class II	35.0 – 39.9	Very high risk
Obese Class III	40.0 and above	Extremely high risk

Limitations of BMI

BMI is a screening tool, not a diagnostic test. It has known limitations:

• Muscle vs fat: Athletes and bodybuilders with high muscle mass may be classified as overweight despite low body fat.
• No distribution info: Where you carry fat matters. Belly fat (visceral) is more dangerous than hip/thigh fat.
• Age differences: Older adults naturally lose muscle and bone density, so a “normal” BMI may mask low muscle mass.
• Ethnic variations: Asian populations have higher health risks at lower BMI thresholds. Some guidelines recommend 23 as the overweight cutoff for Asian adults.
• Pregnancy: BMI is not applicable during pregnancy.

Better Metrics to Pair With BMI

• Waist circumference: Over 88 cm (35 in) for women or 102 cm (40 in) for men indicates higher health risk.
• Waist-to-hip ratio: A better predictor of heart disease than BMI alone.
• Body fat percentage: Directly measures fat vs lean mass. Healthy range: 10–20% (men), 18–28% (women).
• BMR: Your Basal Metabolic Rate tells you how many calories your body burns at rest.

When to Check Your BMI

• Annual check-ups: Track changes over time
• Before starting a diet or exercise program: Get a baseline
• After significant weight change: See which category you fall into
• Insurance and medical forms: Many forms still ask for BMI

Calculate your BMI now with the free BMI Calculator and pair it with other health metrics for a complete picture.