Free BMI Calculator (+ Guide)

What is a BMI calculator?

A BMI calculator divides your weight by your height squared. The result is one number that compares weight across heights.

The formula is BMI = weight in kg ÷ (height in m)². In pounds and inches, it's 703 × pounds ÷ inches².

How to use the BMI calculator

You only need your height and weight, and every health calculator here shares them.

Your numbers stay in this browser.

The BMI ranges

These are the World Health Organization's bands for adults.

A WHO expert group suggested lower points for action in Asian populations in 2004, because health risks there rise at lower BMIs.

A worked example

Here's the example the calculator loads when you press Try an example.

At 178 cm and 78 kg, BMI is 78 ÷ 1.78² = 24.6. That's in the healthy range, close to its top.

The healthy range at that height runs from 58.6 to 78.9 kg, so there's about 1 kg of room before overweight.

Healthy weight by height

Here's the healthy range, a BMI of 18.5 to 24.9, at a few heights.

The calculator shows yours in your own units.

When to look past BMI

BMI is a quick screen, not a full picture.

Muscle weighs more than it looks

A lifter at a BMI of 27 may have little fat. The body fat calculator shows what your weight is made of.

Where fat sits matters

Fat around the waist carries more risk than fat elsewhere. A waist measurement adds what BMI leaves out.

Age and build

BMI doesn't adjust for age, frame or sex. Use it with your other numbers, not alone.

Mistakes to avoid

These are the common ways BMI gets misread.

• Treating a BMI of 25 as a health problem on its own
• Ignoring BMI because you train, without checking body fat
• Using adult bands for children, who have their own charts
• Chasing a number instead of strength, fitness and energy

Use BMI as one number among a few.

Strength over the scale

Your weight matters less than what it's made of.

The longevity test checks the things that predict how well you age, like your fitness and strength.

Who is the BMI calculator for?

It's for any adult who wants a quick check of weight for height, and these tools go further.

• Body fat calculator – for what your weight is made of
• Ideal weight calculator – for a goal weight range
• Calorie calculator – for a target to reach it
• Longevity test – for the checks that matter more as you age
• Biological age calculator – for how old your body really is

Check your BMI here, then measure your body fat for the fuller picture.

More health calculators

Every health calculator reads the same "You", so you only enter yourself once.

The body fat calculator uses the same height and weight, plus a tape measure.