Updated · Built and checked by the PlinzoTools team, formulas tested against published sources
Calculate your Body Mass Index and see which weight category it falls into.
22.9
Body Mass Index (BMI) is the standard screening metric the World Health Organization uses to classify weight relative to height. This tool calculates your BMI instantly and shows which of the four standard categories it falls into.
Enter your weight in kilograms and height in centimeters. Your BMI and category update instantly.
BMI = weight (kg) / height (m)²
Categories: Underweight <18.5, Normal weight 18.5-24.9, Overweight 25-29.9, Obese ≥30.
BMI is a population-level screening tool, not a diagnosis -- it doesn't distinguish muscle from fat, so very muscular people (e.g. athletes) can show an inflated BMI despite low body fat. For a more direct estimate of body composition, see the Body Fat Percentage Calculator. This tool is for general information, not medical advice.
Take a hypothetical adult who weighs 70 kg and is 175 cm tall, which are also the values the calculator opens with. The tool converts the height to 1.75 metres, squares it to get 3.0625, and divides 70 by that number. The result is 22.9, shown with one decimal place, and the label reads Normal weight. Now imagine the same person at 90 kg: 90 divided by 3.0625 is about 29.4, which falls in the Overweight band, just under the Obese boundary. Because the formula squares height, the same weight can land in different categories for people of different heights, which is exactly the point of using an index rather than raw weight.
BMI = weight in kg / (height in cm / 100) squared
The tool compares the unrounded BMI with 18.5, 25 and 30. Anything below 18.5 is Underweight, from 18.5 up to but not including 25 is Normal weight, from 25 up to but not including 30 is Overweight, and 30 or more is Obese. Since the check uses the full value, a BMI that displays as 25.0 might still be labeled Normal weight if the true value is 24.96, because the display rounds and the category does not. If you are close to a boundary, do not read much into which side you land on; the difference of a fraction of a point is smaller than everyday measurement error.
BMI describes how heavy you are for your height. It says nothing about where weight is carried, how much of it is muscle, or how healthy your blood tests and habits are. A person with a lot of muscle can register as Overweight, while someone with little muscle and a higher share of body fat can register as Normal. Age, sex, ethnicity, pregnancy and growth stage also change how the number should be read, and standard adult categories are not designed for children and teenagers, whose results are judged against age-specific charts by clinicians.
Use the result as one data point. Tracking it over months tells you more than a single reading. If your category changes unexpectedly, or you are concerned about weight, eating or fitness, speak with a doctor or registered dietitian. This page is for general education and does not diagnose or treat anything.
No -- it's a useful population screening tool but doesn't account for muscle mass, bone density, or body fat distribution, so it can misclassify very muscular or very lean individuals.
18.5-24.9 is classified as "Normal weight" by the WHO's standard thresholds, though healthy ranges can vary by individual factors like age, sex, and muscle mass.
No -- pair it with other metrics like the Waist-to-Height Ratio Calculator or body fat percentage, and consult a healthcare provider for a full picture.
The display is rounded to one decimal, but the category uses the unrounded value. A true value of 24.96 shows as 25.0 and is still labeled Normal weight.
No. The tool expects kilograms and centimetres, so convert first. Mixing units gives a meaningless result.
The categories shown are adult thresholds. Children and teenagers are usually assessed against age and sex growth charts by a healthcare professional.
Both weight and height must be greater than zero for the formula to work, so the result area stays empty until they are.
Reference: Centers for Disease Control and Prevention