BMI

BMI Calculator

Details

How to use BMI Calculator

What the tool does, how to run it, and what to expect from the result.

How to calculate BMI

Enter your weight in kilograms and your height in centimeters. The calculator converts the height to meters, divides your weight by the square of that number, and shows the result to one decimal place together with the adult category it falls into.

Everything runs in your browser, so the numbers you type are never sent anywhere. Treat the result as one crude summary statistic rather than a verdict, because the formula has no way of knowing what your kilograms are made of.

  • Enter your weight in kilograms (convert from pounds by dividing by 2.205).
  • Enter your height in centimeters (5 feet 9 inches is 175 cm).
  • Read the BMI number, which updates as you type.
  • Read the category, which uses the standard adult thresholds of 18.5, 25, and 30.
  • If you are muscular, very tall, very short, pregnant, or under 20, treat the category as unreliable and use a waist measurement alongside it.

What the BMI categories mean here

The tool prints one of four labels. Below 18.5 it says Underweight, from 18.5 up to 25 it says Normal weight, from 25 up to 30 it says Overweight, and 30 or above it says Obese. Those are the widely used adult bands, and the boundary values sit at the bottom of each band, so a BMI of exactly 25.0 reads as Overweight.

A few worked examples make the scale concrete. 70 kg at 175 cm gives 22.9 and reads Normal weight. 60 kg at 165 cm gives 22 and reads the same. 90 kg at 175 cm gives 29.4 and reads Overweight. 100 kg at 180 cm gives 30.9 and crosses into Obese. The gap between the last two is 10 kg of body weight and one label.

Because the display drops trailing zeros, a BMI of 22.0 appears simply as 22. That is a formatting choice and not a different calculation.

  • Under 18.5: Underweight
  • 18.5 to just under 25: Normal weight
  • 25 to just under 30: Overweight
  • 30 and above: Obese
  • With both fields empty or at zero, the category reads Enter values instead of guessing.

Where BMI stops describing a person

BMI is a ratio of mass to height squared, and it is blind to what the mass is. Muscle is denser than fat, so trained bodies carry more kilograms at the same height and routinely land a band higher than their body composition warrants. The same number can describe two very different people.

The squaring is also asymmetric. Height is squared and weight is not, so tall people are pushed upward and short people downward relative to their actual body fat. The adult bands themselves come mostly from data on people of European descent, and several health bodies use a lower overweight threshold, around 23, for people of South Asian descent.

If the number here worries or reassures you, a waist measurement is the cheap next step. Waist circumference and waist-to-height ratio track cardiometabolic risk better than BMI does, and they take ten seconds with a tape measure.

Tips

Getting a better result out of BMI Calculator

Specific settings and thresholds, not general advice.

  • BMI was designed by a 19th-century statistician to describe populations, not individuals, and it cannot tell muscle from fat, which is why a lean athlete routinely lands in the overweight band while a sedentary person with the same number carries far more fat.
  • The math is weight in kilograms divided by height in meters squared, shown to one decimal place. The category thresholds are the standard adult bands: under 18.5 underweight, 18.5 to 24.9 normal, 25 to 29.9 overweight, 30 and above obese.
  • Because height is squared and weight is not, BMI systematically flags tall people as heavier than they are and short people as lighter. A 2 meter frame with a healthy amount of muscle can cross 25 without any excess fat at all.
  • The bands are drawn from data on adults of European descent. Several health bodies use a lower overweight threshold, around 23, for people of South Asian descent, because cardiometabolic risk rises at a lower BMI in those populations.
  • A waist measurement, or a waist-to-height ratio, predicts cardiometabolic risk better than BMI does and takes ten seconds with a tape measure. If the BMI number here worries or reassures you, that is the number worth checking next.
  • One BMI reading says very little. A trend across months, read next to a waist measurement and how your clothes fit, says considerably more than any single morning on the scale.
Limits

What BMI Calculator does not do

The honest boundary, so you do not lose time finding it yourself.

  • Metric inputs only: kilograms and centimeters. There is no pounds, feet, or inches entry, and no sex, age, or body composition field.
  • Adults only. BMI for anyone under 20 has to be read against age and sex percentile charts, which this calculator does not do.
  • It has no idea about body composition, pregnancy, ethnicity, or fat distribution, so the category it prints describes a ratio and not your health.
  • It is an educational estimate, not medical advice. Individual bodies vary widely at the same BMI, and a doctor or registered dietitian should guide any real decision about your weight, diet, or training.
At a glance

Who BMI Calculator is for

A quick way to understand who this helps, what it solves, and where it connects next.

Best fit

People tracking fitness, nutrition, and everyday health goals.

Ideal for

A quick, private health estimate without an account or app install.

FAQ

Common questions

Short answers for the questions people usually have before trying a utility like this.

What is my BMI if I weigh 70 kg and I am 175 cm tall?

22.9. The calculator turns 175 cm into 1.75 meters, squares it to 3.0625, and divides 70 by that. The result lands in the normal weight band, which runs from 18.5 up to 25.

How is BMI calculated?

Weight in kilograms divided by height in meters squared. That is the whole formula. This tool takes your height in centimeters, divides by 100 to get meters, squares it, and divides your weight by the result, then rounds to one decimal place.

What is a healthy BMI?

The normal weight band runs from 18.5 up to 25, and this tool labels anything in that range Normal weight. It is a band and not a target: plenty of healthy people sit near either edge of it, and the band says nothing about how much of your weight is muscle.

What BMI is considered overweight?

25 up to just under 30 prints as Overweight here. A BMI of exactly 25.0 reads as Overweight, because the boundary belongs to the higher band. At 175 cm, that boundary is about 76.6 kg.

What BMI counts as obese?

30 and above. At 180 cm that is roughly 97.2 kg, so 100 kg at 180 cm gives 30.9 and prints Obese. The label is a statistical category and not a clinical assessment of any individual.

Is BMI different for men and women?

The adult bands are the same for both, which is why this calculator has no sex field. Men and women do differ in average body composition at the same BMI, and that difference is one of the reasons the index is a blunt instrument for individuals.

Why does BMI say I am overweight when I am clearly not?

Because BMI is a ratio of mass to height and knows nothing about what the mass is made of. Muscle is denser than fat, so a well-trained body carries more kilograms per centimeter. This is the single most common and best-documented failure mode of the index.

Can I use this for a child?

No. Children and teenagers are assessed with BMI-for-age percentiles, which compare the value against a growth reference for their exact age and sex. The fixed adult bands here will mislabel them.

Does it accept pounds and feet?

No. The two fields are kilograms and centimeters. Convert first if your scale reads in pounds: divide pounds by 2.205, and multiply feet by 30.48 then add 2.54 per inch.

Why does my BMI show as 22 with no decimal?

The result is rounded to one decimal place and trailing zeros are dropped, so a BMI of 22.0 displays as 22. Nothing about the calculation changes, it is only how the number is printed.

Is BMI useless then?

It is useful for what it was built for, which is comparing groups of people cheaply, and it correlates well with body fat across a whole population. It becomes unreliable exactly when you apply a population statistic to one person, which is what everyone does with it.

What should I measure instead?

Waist circumference or waist-to-height ratio is the usual next step, because abdominal fat is what drives cardiometabolic risk. Keeping your waist under half your height is a simple and well-supported target, and it is one that BMI cannot capture.

What should I do with the number after I read it?

Nothing dramatic on its own. If you want a calorie figure to work from, the TDEE calculator and the calorie calculator estimate daily energy needs, and the water intake calculator handles hydration. For anything that touches your health, take the number to a doctor or a registered dietitian rather than acting on it alone.

Is the BMI calculator free?

Yes. It is completely free to use, with no signup, no account, and no paywall.

Does it stay local?

Yes. The height and weight you enter are processed entirely in your browser and never uploaded.

Are the results medical advice?

No. The output is a general estimate built from a standard formula and population averages, and estimates vary between individuals. For decisions about your health, diet, or training, check with a doctor or registered dietitian.

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