How is BMI calculated?

BMI is calculated by dividing your weight in kilograms by the square of your height in meters: BMI = weight (kg) / height (m)². In imperial units: BMI = (weight in lbs × 703) / (height in inches)².

What are the BMI categories?

The standard WHO BMI categories for adults are: Underweight (below 18.5), Normal weight (18.5–24.9), Overweight (25–29.9), Obese Class I (30–34.9), Obese Class II (35–39.9), and Obese Class III (40 and above).

Is BMI accurate for everyone?

BMI is a useful screening tool but has limitations. It does not distinguish between muscle and fat mass, so athletes or very muscular people may have a high BMI despite being healthy. It also does not account for age, sex, bone density, or fat distribution. Always consult a healthcare professional for a complete assessment.

What is a healthy BMI range?

For most adults, a BMI between 18.5 and 24.9 is considered healthy. However, optimal BMI can vary by age, sex, and ethnicity. A healthcare provider can help interpret your BMI in context.

How do I find my healthy weight range?

Your healthy weight range is based on having a BMI between 18.5 and 24.9. For a given height, you can calculate the range: Minimum healthy weight = 18.5 × height(m)², Maximum healthy weight = 24.9 × height(m)². This calculator shows your healthy range automatically.

Free & Instant

BMI Calculator

Calculate your Body Mass Index from your height and weight. Get your BMI category, healthy weight range, and a visual breakdown — instantly.

Height

Weight

Your BMI

Under

Normal

Over

Obese

Note: BMI is a screening tool, not a diagnostic measure. It does not account for muscle mass, bone density, age, sex, or fat distribution. Consult a healthcare professional for a complete health assessment.

Height

Weight

lbs

Your BMI

Under

Normal

Over

Obese

Understanding Body Mass Index (BMI)

Body Mass Index is a simple numerical value derived from your height and weight. It was developed in the early 19th century by mathematician Adolphe Quetelet and is now widely used by the World Health Organization (WHO) as a quick screening method for weight categories that may lead to health problems.

The BMI Formula

BMI uses a straightforward formula. In metric units, you divide your weight in kilograms by the square of your height in meters. In imperial units, you multiply the result by a conversion factor of 703.

Metric: BMI = weight (kg) ÷ height (m)²
Imperial: BMI = (weight (lbs) × 703) ÷ height (in)²

Example: Height = 175 cm (1.75 m), Weight = 70 kg
BMI = 70 ÷ (1.75 × 1.75) = 70 ÷ 3.0625 = 22.9 (Normal weight)

BMI Categories (WHO Standard)

The World Health Organization defines the following BMI categories for adults aged 20 and over. These thresholds apply equally to men and women.

Category	BMI Range
Underweight	Below 18.5
Normal weight	18.5 – 24.9
Overweight	25.0 – 29.9
Obese Class I	30.0 – 34.9
Obese Class II	35.0 – 39.9
Obese Class III	40.0 and above

Limitations of BMI

While BMI is a useful population-level screening tool, it has important limitations at the individual level. It doesn't differentiate between muscle and fat — a muscular athlete may have a "overweight" BMI despite having low body fat. It also doesn't account for fat distribution (belly fat is riskier than hip fat), age, sex, or ethnicity. For a fuller picture of health, other measures like waist circumference, body fat percentage, and blood markers are recommended alongside BMI.

Healthy Weight Range

Given your height, this calculator automatically computes your healthy weight range based on the normal BMI range of 18.5–24.9. This gives you a concrete target to aim for, rather than just a category label.

Min healthy weight = 18.5 × height(m)²
Max healthy weight = 24.9 × height(m)²

Frequently Asked Questions

BMI is your weight in kilograms divided by the square of your height in meters. In imperial units, multiply your weight in pounds by 703, then divide by height in inches squared.
The WHO categories for adults are: Underweight (below 18.5), Normal weight (18.5–24.9), Overweight (25–29.9), Obese Class I (30–34.9), Obese Class II (35–39.9), and Obese Class III (40+).
BMI is a useful screening tool but has limitations. It doesn't distinguish between muscle and fat, so athletes may have a high BMI despite being healthy. It also doesn't account for age, sex, bone density, or fat distribution. Always consult a healthcare professional for a complete assessment.
For most adults, a BMI between 18.5 and 24.9 is considered healthy. However, the optimal range can vary by age, sex, and ethnicity. A healthcare provider can help interpret your BMI in context.
Your healthy weight range is calculated from a BMI of 18.5 to 24.9 for your height. Multiply 18.5 and 24.9 by the square of your height in meters to get the minimum and maximum healthy weights. This calculator shows it automatically.
Yes. For children and teens (ages 2–19), BMI is interpreted using age- and sex-specific percentiles rather than fixed thresholds. This calculator is designed for adults aged 20 and over.