Calculate your Body Mass Index from height and weight, with category guidance and healthy-range targets.

About the BMI Calculator

Body Mass Index is the screening number your doctor, insurer, and most public-health charts start with because it needs only two measurements: height and weight. It does not measure body fat directly, but across large populations it correlates well enough with fat mass to flag whether someone sits in the underweight, healthy, overweight, or obese band. This calculator turns your height and weight into a single figure and then, more usefully, tells you the actual weight range that would put you inside the healthy band for your exact height.

The tool accepts either metric (centimeters and kilograms) or imperial (feet, inches, and pounds) input and converts everything to SI units behind the scenes, so a runner who thinks in pounds and a nurse who charts in kilograms get the same answer. Because the healthy-range output is expressed back in whatever units you chose, you can see at a glance how many pounds or kilograms separate you from the top or bottom of the normal range rather than trying to reverse-engineer it from a bare index number.

Before you enter your numbers

Measure height and weight using consistent units. Select metric or imperial and replace the sample values.

Assumptions and limits

BMI is a screening measure, not a diagnosis or direct measurement of body fat. Adult categories are not appropriate for children, and pregnancy and high muscle mass require different interpretation.

Check your result

72 kg ÷ (1.75 m × 1.75 m) = 23.51, displayed around 23.5. Changing units should describe the same measurements, not merely keep the same numeric values.

How the BMI Calculator works

BMI uses the metric formula weight in kilograms divided by height in meters squared. Imperial entries are converted first: height in feet and inches becomes meters by multiplying total inches by 0.0254, and pounds become kilograms by multiplying by 0.453592. With a height of 1.75 m the denominator is 1.75 x 1.75 = 3.0625, and every kilogram of body weight is divided by that fixed number.

The result is sorted into the standard World Health Organization adult bands: under 18.5 is underweight, 18.5 up to 24.9 is normal, 25 up to 29.9 is overweight, and 30 or above is obese. To produce the healthy weight range the calculator runs the formula in reverse, multiplying 18.5 and 24.9 by your height-squared value to find the lightest and heaviest weights that still land inside the normal band, then converts those back to your chosen units.

Worked example

Enter 175 cm and 72 kg in metric mode. Height squared is 3.0625, so BMI is 72 / 3.0625 = 23.5, which falls in the Normal band. The healthy range for that height comes from 18.5 x 3.0625 = 56.7 kg at the low end and 24.9 x 3.0625 = 76.3 kg at the high end.

That tells the user they have roughly 4 kg of headroom before crossing into the overweight band at 25 (which would be about 76.6 kg) and are comfortably above the underweight threshold. Switching to imperial, the same person is about 5 ft 9 in and 159 lb, with a healthy range of roughly 125 lb to 168 lb.

Tips & common mistakes

BMI overestimates fat in very muscular people; a lean powerlifter can score 27 yet carry low body fat, so treat a high number as a prompt to check waist circumference or body-fat percentage, not a diagnosis.
It underestimates risk in older adults who have lost muscle, and it is not valid for children, pregnant women, or athletes in weight-class sports use age- and sex-specific percentile charts instead.
Measure height without shoes and weigh yourself at a consistent time, ideally in the morning after using the bathroom, so day-to-day water shifts do not move the number.
Waist-to-height ratio (keep your waist under half your height) catches central fat that BMI misses, so pair the two if your index sits near a band boundary.

BMI Calculator: frequently asked questions

Why is BMI the same formula for men and women?

The core index deliberately ignores sex because it is a population screening tool, not a body-composition measurement. Women naturally carry more essential fat than men at the same BMI, so a given number implies slightly higher body fat for women. That is why BMI is best used as a first filter and paired with waist measurement or a body-fat estimate for anything more precise.

Is a BMI of 23.5 healthy?

Yes. Anything from 18.5 up to 24.9 is inside the normal band, and 23.5 sits in the middle of it. Most large studies show the lowest all-cause mortality clusters in the low-to-mid 20s, so 23.5 is a comfortable, sustainable place to be for most adults.

How much weight would push me from normal into overweight?

Multiply 25 by your height in meters squared to find the exact weight at the boundary. For someone 1.75 m tall that is 25 x 3.0625 = 76.6 kg, so the tool's healthy-range top of 76.3 kg is just below it. Anything above roughly 76.6 kg crosses into the overweight band.

Does muscle make BMI inaccurate?

It can. Muscle is denser than fat, so athletes and heavy lifters weigh more for their height and can score in the overweight or obese range while being metabolically healthy. If you train seriously, verify with a body-fat method such as calipers, a DEXA scan, or bioelectrical impedance before acting on the number.

Can I use this calculator for my child?

No. Children and teens are assessed with age- and sex-specific BMI-for-age percentiles rather than the fixed adult cut-offs, because healthy body composition changes rapidly during growth. Use a pediatric growth chart or ask your pediatrician for the correct percentile.

Use the result in your next decision

Workout Log: Record activity rather than interpreting one screening number as a fitness assessment.

Sources and further reading

These references explain the specified topic; they are not endorsements or evidence that a professional has reviewed this tool.

CDC: Adult BMI — Screening limitations and adult categories; consult a clinician for personal interpretation.

BMI Calculator