BMI Calculator

1. Choose your unit system. Select Imperial (pounds and feet/inches) or Metric (kilograms and centimeters). Both give the same result.
2. Enter your sex and age. These are used to estimate body fat percentage alongside your BMI. The BMI formula itself is the same for all adults.
3. Enter your height. Measure without shoes. For Imperial, enter feet and inches separately. For Metric, enter total centimeters.
4. Enter your weight. Weigh yourself in the morning before eating for the most consistent reading.
5. Read your result. The calculator shows your BMI, category, BMI Prime, estimated body fat, and the healthy weight range for your height. The color gauge shows exactly where you fall across the full BMI spectrum.

Body Mass Index divides your weight by your height squared. That single number places you on the scale the World Health Organization uses to classify weight status across populations.

Metric:    BMI = weight (kg) / height (m)²

Imperial:  BMI = 703 × weight (lbs) / height (in)²

• weight = your body weight in kilograms, or pounds (Imperial)
• height = your height in meters, or total inches (Imperial)
• 703 = a unit conversion constant for working in pounds and inches

Worked example (Imperial): Someone who is 5'10" (70 inches) and weighs 175 lbs:

BMI = 703 × 175 / (70²) = 123,025 / 4,900 = 25.1 → Overweight

Worked example (Metric): Same person at 178 cm and 79.4 kg:

BMI = 79.4 / (1.78²) = 79.4 / 3.168 = 25.1 → Overweight

The healthy weight range for a 5'10" person is 129 to 173 lbs (BMI 18.5 to 24.9).

BMI Prime

BMI Prime is your BMI divided by 25 (the upper limit of normal). A BMI Prime of 1.0 means you are at the exact boundary of normal and overweight. Values below 1.0 are in the normal or underweight range; above 1.0 is overweight or obese. It makes the distance from the healthy threshold immediately readable: a BMI Prime of 1.20 means you are 20% above the normal cutoff.

BMI Prime = BMI / 25

Example: BMI 25.1 → BMI Prime = 25.1 / 25 = 1.004

Estimated Body Fat (Deurenberg Formula)

BMI alone does not measure fat. The Deurenberg formula adds age and sex to estimate body fat percentage:

Men:   Body Fat % = (1.20 × BMI) + (0.23 × Age) − 16.2
Women: Body Fat % = (1.20 × BMI) + (0.23 × Age) − 5.4

This estimate has a margin of error of around 4 percentage points. For a precise body fat reading, use a DEXA scan or hydrostatic weighing.

A BMI between 18.5 and 24.9 is considered healthy for most adults. But two people with the same BMI can have very different health profiles depending on where they carry fat, how much muscle they have, and their age.

Health Risks by BMI Category

BMI and Cancer Risk

The American Cancer Society links excess body weight to at least 13 types of cancer, including breast (postmenopausal), colon, endometrial, kidney, and pancreatic cancers. Being overweight or obese is the second leading preventable cause of cancer in the US after smoking. Maintaining a BMI below 25 significantly reduces cancer risk across all of these categories.

BMI Limitations

About 30% of people with a normal BMI have metabolic risk factors like high blood pressure or elevated triglycerides. Meanwhile, some individuals in the overweight range have no risk factors at all. BMI misses body composition entirely: two people at BMI 27 may have completely different amounts of fat versus muscle.

• Athletes and muscular people: Muscle is denser than fat. A 200-pound athlete with 10% body fat can have the same BMI as a sedentary person with 35% body fat.
• Older adults: Muscle mass decreases with age. An elderly person may have a normal BMI while carrying a high proportion of body fat.
• Asian adults: Research shows that people of Asian descent have higher metabolic risk at lower BMI values. Many health organizations use lower thresholds: overweight at BMI 23 and obese at BMI 27.5 for Asian populations.
• Sex differences: Women naturally carry 6 to 11 percentage points more body fat than men at the same BMI. The formula and cutoffs do not account for this.

Waist Circumference: A Better Abdominal Risk Indicator

Fat stored around the abdomen (visceral fat) is more metabolically dangerous than fat stored in the hips and thighs. Waist circumference thresholds that signal elevated cardiovascular risk:

If your BMI is borderline (25 to 30), waist circumference is the most useful next measurement. You can also pair BMI with our body fat calculator and ideal weight calculator for a fuller picture.