What is a healthy BMI range?

The World Health Organization defines a normal BMI as 18.5–24.9. Below 18.5 is underweight, 25–29.9 is overweight, and 30 or above is obese.

Is BMI accurate for everyone?

BMI is a useful screening tool but doesn't distinguish between fat and muscle. Athletes and very muscular people may register a high BMI despite low body fat. Always pair BMI with other measurements.

Should I use BMI for children?

Standard BMI ranges apply to adults aged 20+. For children and teens, use age-and-sex-specific BMI percentiles.

BMI Calculator

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Body Mass Index is a quick screen for whether your weight is in a healthy range for your height. Enter your measurements below in metric or imperial units.

Height

Weight

What is BMI?

Body Mass Index is a single number that compares your weight to your height. The formula is simple — weight in kilograms divided by height in metres squared — and the result places you in one of four categories defined by the World Health Organization. It was popularised in the 1970s as a fast public-health screening tool and remains the most widely-used weight indicator today.

How to use this calculator

Pick your unit system using the toggles above.
Enter your height and weight.
Click Calculate BMI to see your value, category, and a position on the BMI scale.

The limitations of BMI

BMI was designed for populations, not individuals. It doesn't distinguish fat from muscle, so a heavily-trained athlete can score "overweight" or "obese" despite low body fat. It also doesn't account for body-fat distribution — visceral fat around organs is far more harmful than subcutaneous fat — or for differences across ethnicities and age groups. Treat your BMI as one data point among several. Waist-to-hip ratio, body-fat percentage, fitness levels, and lab markers (cholesterol, blood sugar) collectively give a much more accurate picture of metabolic health.

How BMI is calculated

The Body Mass Index formula is simple: BMI = weight (kg) / height² (m²). For someone who is 170 cm tall and 70 kg: BMI = 70 / (1.70 × 1.70) = 70 / 2.89 = 24.2. The same calculation in imperial units uses a factor of 703: BMI = (weight in lb × 703) / height² (in). This calculator handles both systems automatically — switch between metric and imperial using the toggle at the top.

BMI categories used in this calculator

The standard WHO classification thresholds are:

Underweight: BMI below 18.5
Normal weight: BMI 18.5 to 24.9
Overweight: BMI 25 to 29.9
Obese (Class I): BMI 30 to 34.9
Obese (Class II): BMI 35 to 39.9
Severely obese (Class III): BMI 40 and above

BMI thresholds for South Asian populations

The Indian Council of Medical Research (ICMR) and the World Health Organization recommend lower BMI cutoffs for Indians and other South Asian populations because cardiovascular and metabolic disease risk rises at lower BMI than in European populations. Per ICMR's revised 2023 guidelines, the thresholds for Indians are: normal weight 18.0 to 22.9, overweight 23.0 to 24.9, obese 25.0 and above. These are 2 BMI points lower than the WHO global cutoffs at the overweight and obese thresholds. If you are of Indian or South Asian ethnicity and your BMI falls between 23 and 25, your cardiovascular risk profile is closer to "overweight" than "normal."

What BMI does and does not measure

BMI is a screening tool, not a diagnostic measure. It does not distinguish between muscle and fat, so very muscular people (athletes, bodybuilders) will register as "overweight" or "obese" without actually carrying excess fat. BMI also does not measure where fat is distributed — abdominal fat is more strongly linked to disease risk than peripheral fat. For a more complete picture, combine BMI with waist circumference (men: under 90 cm safe, women: under 80 cm safe per Asian standards), waist-to-hip ratio, and body fat percentage. Children and adolescents use age-and-sex-specific BMI percentiles, not the adult thresholds shown here.

Disclaimer

This calculator is for personal informational purposes only and does not constitute medical advice. BMI is a screening tool and should not be used to diagnose any health condition or to make any medical decision. Consult a qualified medical professional — a doctor, registered dietician, or certified clinical nutritionist — before starting any weight management program, especially if you have a history of eating disorders, cardiovascular disease, diabetes, or are pregnant. Children, adolescents, pregnant women, athletes, and elderly people often have special considerations that this calculator cannot account for.

Frequently asked questions

Is BMI accurate for athletes?

Often not — muscle is denser than fat, so muscular individuals frequently land in the "overweight" category despite being healthy. Athletes should use body-fat percentage measurements instead.

What about children?

Children and teenagers under 20 should use age- and sex-specific BMI percentiles, not the adult ranges shown here.

Should I aim for a "Normal" BMI?

For most adults, yes — but speak to a healthcare provider before making major changes. Sustainable weight changes take months, not days.

Why are the categories the way they are?

The cutoffs are based on epidemiological data linking BMI to mortality and chronic-disease risk. The thresholds are rounder approximations of inflection points where risk increases.