What is a healthy BMI?

The World Health Organization defines a healthy BMI as 18.5 to 24.9. Below 18.5 is underweight, 25–29.9 is overweight, and 30 or above is obese.

How is BMI calculated in metric units?

BMI = weight (kg) ÷ height (m)². For example, a person weighing 70 kg at 175 cm has a BMI of 70 ÷ (1.75 × 1.75) = 22.9.

Is BMI an accurate measure of health?

BMI is a useful screening tool but has limitations. It does not distinguish between muscle and fat, and can misclassify athletes as overweight or older adults as normal weight when they have high body fat.

Is my data sent to a server?

All calculations are pure JavaScript running in your browser. Our servers are not involved at any point.

BMI calculator, metric (kg / cm)

Enter your weight in kilograms and height in centimetres to calculate your BMI and see your WHO weight category instantly. All calculations run locally in your browser.

Height (cm)

Weight (kg)

How it works

Centimetres are divided by 100 to get height in metres, then the WHO formula weight(kg) / height(m)^2 produces your BMI directly in metric units with no unit conversion needed. The resulting number is matched against the WHO thresholds (under 18.5, 18.5 to 24.9, 25 to 29.9, and 30 or above) so the category label updates instantly as you adjust either input.

Processing runs in your browser

All calculations happen locally in your browser tab. Our servers are not involved at any point.

Technical specification

The BMI formula was standardised by the WHO Technical Report Series 894 (2000): BMI = weight(kg) / height(m)². WHO classifies BMI into four categories for adults: Underweight (<18.5), Normal weight (18.5–24.9), Overweight (25.0–29.9), and Obese (≥30.0). BMI does not distinguish between muscle and fat mass and is intended as a population-level screening tool, not an individual diagnostic.

Formula: weight(kg) / height(m)²
Standard: WHO Technical Report Series 894 (2000)
Normal range: 18.5 – 24.9
Browser API: Pure JavaScript arithmetic. No library

Related operations

To estimate daily energy needs, try the calorie calculator. For body composition with circumference measurements, use the body fat calculator. To find a reference weight range for your height, see the ideal weight calculator.

Frequently asked questions

What is a healthy BMI?: The World Health Organization defines a healthy BMI as 18.5 to 24.9. Below 18.5 is underweight, 25–29.9 is overweight, and 30 or above is obese.
How is BMI calculated in metric units?: BMI = weight (kg) ÷ height (m)². For example, a person weighing 70 kg at 175 cm has a BMI of 70 ÷ (1.75 × 1.75) = 22.9.
Is BMI an accurate measure of health?: BMI is a useful screening tool but has limitations. It does not distinguish between muscle and fat, and can misclassify athletes as overweight or older adults as normal weight when they have high body fat.
Is my data sent to a server?: All calculations are pure JavaScript running in your browser. Our servers are not involved at any point.

Last reviewed May 26, 2026