Health & Fitness Calculators

BMI Calculator

BMI Calculator divides weight in kilograms by squared height in metres. Body mass index is a population-level screening measure, not a direct measurement of body fat, fitness, or health. It can misrepresent muscular people, older adults, pregnancy, and individual body composition, and adult thresholds should not be applied to children without age- and sex-specific growth references.

Runs locally — files stay on your device

Weight (kg)

Height (cm)

Quick answer

How is BMI calculated?

Divide weight in kilograms by height in metres squared.

Formula: BMI = weight (kg) ÷ height² (m²)

BMI relates body mass to squared height

BMI expresses kilograms per square metre. For adults, commonly used screening categories place 25 and above in the overweight range and 30 and above in the obesity range, but BMI remains a surrogate marker and should be interpreted with other clinical and contextual information.

How it works

Enter measured weight and height in the displayed metric units. Treat the result as one screening value and discuss concerns or unexpected results with a qualified healthcare professional who can consider age, medical history, body composition, and other measurements.

Key concepts

BMI is a surrogate, not a body-fat measurement

Two people with the same BMI can have different muscle mass, fat distribution, health history, and risk.

Age-specific assessment matters for children

Child and adolescent interpretation uses growth references rather than fixed adult categories.

When to use it

Check the arithmetic of an adult BMI value.
Understand how weight and height contribute to the index.
Prepare a general screening estimate for discussion with a professional.

When not to use it

Do not diagnose health, body-fat percentage, or fitness from BMI alone.
Do not apply adult cutoffs to children or adolescents.
Do not use the result as individualized weight-loss or treatment guidance.

Worked examples

Adult metric example

Input: Weight 72 kg, height 180 cm
Expected output: BMI 22.2

72 ÷ 1.8² = 22.22.

Same weight at shorter height

Input: 72 kg, 165 cm
Expected output: BMI 26.4

Height is squared, so it substantially changes the index.

Athletic build

Input: High weight from muscle at a given height
Expected output: Potentially elevated BMI

The index cannot distinguish muscle from fat.

Common mistakes

Entering centimetres as metres in the formula

Squaring 180 instead of 1.80 makes the result meaningless. Correction: The interface converts entered centimetres to metres.

Treating a category as a diagnosis

BMI does not assess an individual's complete health. Correction: Interpret it with professional assessment and other relevant measures.

Using adult categories for a child

Growth and development require age- and sex-specific references. Correction: Use an appropriate pediatric growth assessment.

Best practices

Use recent, accurately measured values.
Interpret BMI with health history and other measurements.
Seek professional guidance for medical or nutritional decisions.

Limitations and privacy

This is a population-based estimate for general information, not a diagnosis, treatment plan, or individualized medical or nutrition advice.
BMI does not distinguish fat, muscle, bone, pregnancy, or fat distribution.
Adult screening thresholds are not pediatric growth references.

Inputs and estimates remain in this browser. Toolbox does not store or transmit these health-related values.

Frequently asked questions

Does BMI measure body fat directly?

No. It is a weight-to-height index and only a surrogate marker.

Can muscular people have a high BMI?

Yes. BMI cannot distinguish muscle mass from fat mass.

Should children use adult BMI categories?

No. Children and adolescents require age- and sex-specific growth references.

Is a BMI result a diagnosis?

No. Diagnosis and treatment require broader clinical evaluation.

References

WHO — Obesity and overweight