OnSumoTools

BMI Calculator

A BMI calculator takes your height and weight and returns your body mass index score alongside the standard weight category it falls into. BMI is a screening number, not a diagnosis. It estimates whether your weight falls within a range associated with higher or lower health risks, but it does not measure body fat, muscle mass, or individual health directly.

Your BMI score and what the number actually means.

Unit system

BMI

24.2

Normal

BMI Prime

0.97

Below upper normal boundary

1218.52530354050

Healthy weight range

53.5 kg – 72 kg

For your height (BMI 18.5–24.9)

Distance to boundaries

2.2 kg below overweight

WHO Classification Scale

CategoryBMI Range
Underweight< 18.5
Normal18.5 – 24.9
Overweight25.0 – 29.9
Obese Class I30.0 – 34.9
Obese Class II35.0 – 39.9
Obese Class III≥ 40.0

BMI is a population-level screening tool and is not validated for children under 20 or adults with high muscle mass. For a more complete picture, consider using a body fat calculator. This is not medical advice.

How does the BMI Calculator work step by step?

Body Mass Index divides your weight in kilograms by the square of your height in metres. For imperial units the formula is (weight in pounds / height in inches squared) × 703. The result is classified against six WHO categories: Underweight (below 18.5), Normal (18.5–24.9), Overweight (25–29.9), Obese Class I (30–34.9), Obese Class II (35–39.9), and Obese Class III (40+). The tool also derives a healthy weight range for your height by solving for the weights that produce BMI 18.5 and 24.9, and shows how far your current weight sits from each category boundary. BMI Prime is the ratio of your BMI to the upper normal boundary (24.9); a value below 1.0 means you are in the normal or underweight range.

What does a typical BMI Calculator result look like?

A person weighing 70 kg at 175 cm has BMI = 70 / 1.75² = 22.9 (Normal). Their healthy weight range is 56.7–76.3 kg. They are 13.3 kg above underweight and 5.6 kg below overweight. BMI Prime is 22.9 / 24.9 = 0.92.

Frequently asked questions

  • What is a healthy BMI?

    The World Health Organization defines a healthy BMI as 18.5 to 24.9 for adults. BMI is a population-level screening tool, not a diagnostic measure; muscle mass, age, sex, and ethnicity all affect how the number should be interpreted.

  • Is BMI accurate for athletes?

    BMI overestimates body fat in muscular individuals because muscle is denser than fat. A lean athlete may register as overweight on BMI while having very low body fat. Use body fat percentage tools for a more accurate picture.

  • Does BMI differ by age or sex?

    The BMI formula is the same for all adults, but healthy ranges may differ. Children and teens use age- and sex-specific growth chart percentiles rather than adult BMI cutoffs.

  • Can BMI predict health risks?

    At the population level, high BMI correlates with increased risk of type 2 diabetes, cardiovascular disease, and hypertension. For individuals, waist circumference and body fat percentage add important context that BMI alone cannot provide.

Related tools

What BMI measures

Body Mass Index compares your weight with your height. The formula is weight in kilograms divided by height in meters squared. It was designed for studying populations, and it's a quick screening number. It isn't a diagnosis.

Enter your height and weight and the calculator gives your BMI, your category and the weight range that counts as healthy for your height.

The categories

The World Health Organization sets the standard cutoffs for adults. Under 18.5 is underweight. From 18.5 to 24.9 is the normal range. From 25 to 29.9 is overweight. From 30 up is obese, which is split into three classes as the number climbs.

The tool shows where you sit and how far you are from the next boundary, either way. Seeing that you're 1.5 points from a line is more useful than seeing only a label.

  • Under 18.5: underweight
  • 18.5 to 24.9: normal range
  • 25 to 29.9: overweight
  • 30 and above: obesity classes I, II and III

Where BMI falls short

It can't tell muscle from fat. A strength athlete with lots of muscle can land in the overweight range while having low body fat. It also ignores where weight is carried, and fat around the waist carries more risk than fat on the hips.

Age and sex matter too. Older adults tend to carry more fat at the same BMI than younger ones. For children and teens, adult cutoffs don't apply. Pediatric growth charts use age and sex percentiles.

Some groups have different risk at the same BMI. Several health bodies suggest lower cutoffs for people of Asian descent, for example.

Does it predict health?

At a population level, higher BMI goes along with higher risk for conditions like type 2 diabetes and heart disease. For one person, it's one data point. Blood pressure, blood sugar, cholesterol, fitness and family history tell you a lot more.

Better numbers to pair it with

Waist measurement is easy to take and says something BMI can't. Body fat percentage, if you can estimate it, gives a fuller view. The body fat calculator on this site uses a tape measure and no equipment.

How you feel and what you can do matter too. Can you climb stairs without struggling? Are you sleeping well? Those count.

Use it sensibly

Check once in a while, not daily. Use the result as a conversation starter with a doctor, not as a verdict. If you're worried about your weight, either direction, talk to a professional.

This tool is for general information and doesn't give medical advice. Your numbers stay in your browser.