BMI Calculator

Built by Puja Matharu, Australian Certified Nutritionist Updated 2026-08-02 Free, and nothing you enter leaves your browser

How this is calculated

Body mass index is weight in kilograms divided by height in metres squared.

BMI = weight (kg) ÷ height (m)²

So an 80 kg person at 175 cm: 80 ÷ (1.75 × 1.75) = 26.1

BMI	Category
Under 18.5	Underweight range
18.5 – 24.9	Healthy weight range
25.0 – 29.9	Overweight range
30.0 and above	Obese range

What BMI can't tell you

We'll be straight with you: BMI is the number everyone searches for, and it's not the best measure available. It was designed in the 1830s to describe populations, not to assess individuals, and it has three well-known blind spots.

It can't distinguish muscle from fat. A muscular person can land in the "overweight" band while carrying very little body fat.
It can't tell you where fat is stored — and that turns out to be what matters most. Visceral fat around the organs is far more metabolically active than subcutaneous fat.
It misses "skinny fat" entirely. Clinically termed TOFI — thin outside, fat inside — describes people with a normal BMI and high internal visceral fat. They often carry elevated metabolic risk precisely because a normal BMI means nobody investigates further.

It's also less reliable across some ethnic groups, at the extremes of height, during pregnancy, for children, and for older adults where some additional weight is protective.

The measure we'd actually use

Waist-to-height ratio. The rule is simple enough to not need a calculator: keep your waist to less than half your height. It reflects visceral fat, adjusts for body size, and outperforms both BMI and waist circumference alone as a screening measure for cardiometabolic risk.

That's why this calculator has an optional waist field — enter it and you get both numbers, which is more useful than either alone. For the full picture, including how to measure your waist properly, see the waist-to-height ratio calculator.

What to do with the number

Treat BMI as one screening input among several, not a verdict. If it's outside the healthy range, the useful next step is a blood test rather than a diet — fasting glucose, HbA1c, lipids and blood pressure describe your actual metabolic health far better than a weight-to-height ratio can. Our article on what metabolic health actually means covers the five markers worth tracking.

And if you're in the healthy BMI band but have a large waist, poor energy after meals or a family history of type 2 diabetes, don't let a normal BMI reassure you out of getting tested.

Frequently asked questions

How is BMI calculated?

Weight in kilograms divided by height in metres squared. An 80 kg person at 175 cm has a BMI of 80 divided by 1.75 squared, which is 26.1. The healthy range is 18.5 to 24.9, with 25 to 29.9 classed as overweight and 30 or above as obese.

Is BMI accurate?

It is a useful population screening tool but a limited individual one. It cannot distinguish muscle from fat, cannot tell you where fat is stored, and misses people with normal weight but high internal visceral fat. It is also less reliable across some ethnic groups, in pregnancy, for children and for older adults.

What is a better measure than BMI?

Waist-to-height ratio — keep your waist to less than half your height. It reflects visceral fat around the organs, adjusts for body size, and outperforms both BMI and waist circumference alone as a screening measure for cardiometabolic risk. This calculator has an optional waist field so you can see both.

References

A number is a starting point, not a plan

Our AI nutritionist takes your targets and turns them into meals you'll actually eat — and adjusts as your goals, training and life change.

Try it free Book a consultation

General nutrition information only — not medical advice, diagnosis or treatment. See our health disclaimer.