This BMI calculator computes adult body mass index from weight in kilograms and height in centimeters. BMI is weight divided by height squared, with height converted from centimeters to meters first. The page then labels the result with one of four ranges: Underweight, Healthy range, Overweight, or Obesity range.
Those labels follow the usual adult cutoffs used by the World Health Organization: under 18.5, 18.5 up to 25, 25 up to 30, and 30 or above. BMI is a screening measure for population and clinic use. It is not a diagnosis, it does not measure body fat directly, and it is not the right chart for children, teenagers, or pregnancy. A clinician uses more than a single ratio.
How to use this calculator
- Enter weight in kilograms. Pounds have to be converted before you type.
- Enter height in centimeters, not meters. A height of 1.75 m is entered as 175.
- Press Calculate. The headline is BMI rounded to one decimal. The category uses the unrounded value.
- Read the category line. The calculator also reminds you that BMI is a screening measure, not a medical diagnosis.
How adult BMI is calculated from kilograms and centimeters
Height in centimeters is divided by 100 to get meters. That height is squared. Weight in kilograms is divided by the squared height. For 75 kg and 175 cm, height is 1.75 meters, the square is 3.0625, and 75 / 3.0625 is about 24.49, which displays as BMI 24.5.
The category is chosen from the unrounded value. Below 18.5 is Underweight. From 18.5 up to but not including 25 is Healthy range. From 25 up to but not including 30 is Overweight. 30 or above is Obesity range. A result that rounds to 25.0 on screen can still be Healthy range if the unrounded BMI is under 25.
The form has no field for age, sex, waist circumference, or muscle mass. Those factors change how a clinician reads a number. The arithmetic itself is the same for every adult who enters the same weight and height.
Formula
Height in meters = height in centimeters / 100 BMI = weight in kilograms / (height in meters)² Under 18.5: Underweight 18.5 up to 25: Healthy range 25 up to 30: Overweight 30 or above: Obesity range
The on-screen BMI uses at most one decimal place. The category does not use that rounded text. It uses the full division. That is why the label and the rounded number can sit on different sides of a cutoff.
The World Health Organization describes the adult bands as underweight below 18.5, normal from 18.5 to 24.9, overweight from 25 to 29.9, and obese at 30 and above, with further obese classes at 35 and 40. This tool stops at four labels and calls the 18.5–24.9 band Healthy range. It does not split obesity into classes.
Worked BMI examples
75 kg and 175 cm
Height is 175 / 100 = 1.75 meters. Squared height is 1.75 × 1.75 = 3.0625. BMI is 75 / 3.0625 = 24.4897959…. The calculator shows BMI 24.5 and the category Healthy range, because 24.49 is below 25.
This is the sample built into the form. Changing either input changes both the number and, if you cross a cutoff, the label.
Shorter, heavier, and lighter adults
50 kg and 160 cm: height 1.60, squared height 2.56, BMI 50 / 2.56 = 19.53125. The calculator shows BMI 19.5 and Healthy range. 54 kg and 175 cm: 54 / 3.0625 = 17.63265, shown as BMI 17.6 and Underweight.
92 kg and 180 cm: height 1.80, squared height 3.24, BMI 92 / 3.24 = 28.39506, shown as BMI 28.4 and Overweight. 120 kg and 175 cm: 120 / 3.0625 = 39.18367, shown as BMI 39.2 and Obesity range. The tool does not relabel 39.2 as a separate class III figure. Any BMI of 30 or more gets the same Obesity range label.
Starting from pounds and inches
The form does not accept pounds or feet. Convert first. Multiply pounds by 0.45359237 to get kilograms, and multiply inches by 2.54 to get centimeters. Five feet nine inches is 69 inches, and 69 × 2.54 = 175.26 cm. A weight of 165 pounds is 165 × 0.45359237 = 74.8427 kg.
If you type the rounded values 74.8 kg and 175 cm, BMI is 74.8 / 3.0625 = 24.4245, which displays as BMI 24.4 and Healthy range. Rounding the inputs before you type them moves the result slightly. The calculator is doing the metric formula on whatever you entered, not a hidden imperial formula.
Adult BMI cutoffs used on this page
| Unrounded BMI | Label on this page | Common WHO adult band |
|---|---|---|
| Below 18.5 | Underweight | Underweight |
| 18.5 up to 25 | Healthy range | Normal range, often written 18.5–24.9 |
| 25 up to 30 | Overweight | Overweight, often written 25.0–29.9 |
| 30 and above | Obesity range | Obese, with further classes at 35 and 40 |
What BMI does not tell you
BMI does not distinguish fat from muscle, and it does not locate fat. Two adults with the same BMI can have different waist measurements, fitness, and lab results. Athletes and people with high muscle mass are often misread by the ratio alone. Older adults can lose muscle and still sit in a "healthy" band.
Children and teenagers are interpreted with BMI-for-age percentiles, not these adult cutoffs. Pregnancy changes the meaning of the ratio. Some populations also have different associations between BMI and health risk than the bands imply. This page does not adjust for any of that.
A single BMI is not a treatment plan, a body-fat percentage, or a reason to start or stop a diet. If you are making a medical decision, take the number to a clinician who can use height, weight, and the rest of your history together.
Frequently asked questions
Which units does this BMI calculator accept?
Kilograms for weight and centimeters for height. Do not enter pounds, stones, feet, or meters. A height of 1.75 meters must be typed as 175. Convert pounds to kilograms by multiplying by 0.45359237, and inches to centimeters by multiplying by 2.54.
What do Underweight, Healthy range, Overweight, and Obesity range mean?
They are the four adult bands this tool prints: under 18.5, 18.5 up to 25, 25 up to 30, and 30 or above. The middle band corresponds to the WHO normal range. The tool does not subdivide obesity at 35 or 40.
Can the BMI display 25.0 and still say Healthy range?
Yes. The category uses the unrounded ratio, and the headline rounds to one decimal. A value such as 24.96 is still under 25, so the label is Healthy range, while the headline can round to 25.0.
Is BMI a medical diagnosis?
No. It is a screening ratio of weight to height squared. It does not measure body fat, and it is not a diagnosis of any disease. The calculator states that on the result itself.
Does age or sex change the formula here?
No. The same division is used for every entry. Age and sex matter in how a result is interpreted, especially for children, but this form does not collect them and does not switch formulas.