Free calculator

BMI Calculator

This BMI Calculator uses your weight and height to calculate your Body Mass Index - a widely used measure to check whether your weight falls in a healthy range. Designed for Australian users with metric units (kg and cm).

Enter your details

Weight

Height

Your BMI

Example

Example figures, not your own. Worked for an adult of 82 kg and 178 cm. Enter your own details and press Calculate.

Body Mass Index

25.9

Overweight

BMI Scale

Underweight

< 18.5

Normal

18.5 – 24.9

Overweight

25 – 29.9

Obese

30+

How It Works

BMI is calculated by dividing your weight in kilograms by the square of your height in metres: BMI = weight (kg) ÷ height (m)². A BMI under 18.5 is considered underweight, 18.5–24.9 is normal, 25–29.9 is overweight, and 30+ is obese.

How to use it

1Enter your weight in kilograms (kg)
2Enter your height in centimetres (cm)
3Click "Calculate" to see your BMI and weight category

Quick Reference

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

How This Is Calculated

BMI = weight (kg) ÷ height (m)²

weight: = body weight in kilograms
height: = height in metres (cm ÷ 100)

BMI categories are defined by the World Health Organization (WHO). This calculator is for adults 18+ and should not replace professional medical advice.

Frequently Asked Questions

What is a healthy BMI?

A healthy BMI is between 18.5 and 24.9. This range is associated with the lowest risk of weight-related health problems. However, BMI doesn't account for muscle mass, bone density, or fat distribution.

How is BMI calculated?

BMI is your weight in kilograms divided by your height in metres squared. For example, a person weighing 70 kg who is 175 cm tall has a BMI of 70 ÷ (1.75 × 1.75) = 22.9.

Is BMI accurate for everyone?

BMI is a useful screening tool for most adults but has limitations. It may overestimate body fat in muscular individuals and underestimate it in older adults who have lost muscle mass. It should be used alongside other measures like waist-to-hip ratio.

What BMI is considered obese in Australia?

In Australia, a BMI of 30 or above is classified as obese. The Australian Institute of Health and Welfare uses the same WHO categories: underweight (<18.5), normal (18.5–24.9), overweight (25–29.9), and obese (30+).

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