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BMI Calculator

Calculate your Body Mass Index (BMI) and understand what your number means for your health.

Calculate your Body Mass Index

Find your BMI, weight category, and healthy weight range for your height.

cm
or use imperial
kg
yrs

"/> How to use this calculator

  1. Pick your units—Metric (cm, kg) or Imperial (ft/in, lbs) using the toggle above the inputs.
  2. Enter your height in centimeters, or feet and inches if using imperial.
  3. Enter your weight in kilograms (metric) or pounds (imperial).
  4. Optionally add your age—used only to add context to the result.
  5. Click Calculate BMI to see your BMI number, weight category, healthy weight range, and how much you'd need to lose or gain to reach the normal range.
  6. Read the scale—the white marker on the BMI scale shows where you fall on the spectrum from underweight to obese.
HOW IT WORKS

How BMI is calculated and what it really means

Body Mass Index (BMI) is a screening tool developed in the 19th century by Belgian astronomer Adolphe Quetelet. It estimates body fatness from height and weight and is used worldwide because it's simple, free, and roughly correlates with body fat percentage for most adults. The formula produces a single number that places you in one of four categories: underweight, normal weight, overweight, or obese.

The BMI formulas

The calculation differs slightly depending on your unit system:

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

For example, a person who is 175 cm tall and weighs 75 kg has a BMI of 75 ÷ (1.75 × 1.75) = 75 ÷ 3.0625 = 24.5, which sits in the upper end of the normal range.

Category cutoffs and where they come from

The World Health Organization (WHO) defines the standard cutoffs based on large epidemiological studies linking BMI ranges to health risks:

  • Underweight: BMI below 18.5—associated with malnutrition, weakened immunity, and bone loss.
  • Normal weight: BMI 18.5–24.9—generally the lowest risk of metabolic disease.
  • Overweight: BMI 25–29.9—associated with elevated risk of type 2 diabetes, hypertension, and heart disease.
  • Obese: BMI 30 or above—associated with substantially elevated risk of cardiovascular disease, certain cancers, and all-cause mortality.

Some Asian populations use lower cutoffs (23 for overweight, 27.5 for obese) because they tend to accumulate visceral fat and develop metabolic disease at lower BMIs than Caucasian populations.

Healthy weight range and BMI Prime

For any height, you can reverse the BMI formula to find the weight that corresponds to a BMI of 18.5 (lower healthy bound) and 24.9 (upper healthy bound). That range is your "healthy weight zone." The calculator also reports BMI Prime—the ratio of your BMI to the upper limit of normal (24.9). A BMI Prime below 1.0 means you're under the upper normal cutoff; above 1.0 means you're in the overweight or obese range. BMI Prime makes cross-comparisons between individuals of different heights easier.

What BMI can't tell you

BMI is a blunt instrument. It can't distinguish muscle from fat, doesn't measure body fat distribution (visceral belly fat is far more dangerous than subcutaneous fat on the hips), and doesn't account for age, sex, ethnicity, or fitness level. A 250-pound bodybuilder at 6% body fat will register as "obese" despite being in superb condition. An older adult with normal BMI but high body fat and low muscle mass (sarcopenic obesity) may face greater health risks than the BMI suggests. For a fuller picture, pair BMI with waist circumference (above 40 inches for men or 35 inches for women signals elevated risk), body fat percentage from calipers or bioimpedance, and routine metabolic blood work.

When to act on a high BMI

If your BMI is above 25 and you don't carry significant muscle mass, a conversation with your doctor is worthwhile—especially if you also have elevated blood pressure, cholesterol, or blood sugar. Small, sustainable changes (5–10% body weight reduction) can produce outsized health improvements. If your BMI is above 30, structured support from a registered dietitian or medical weight-loss program is often the most effective path. Use the BMI number as a starting point, not a verdict.

"/> Worked example

Scenario: A 30-year-old who is 5'9" (175 cm) tall and weighs 198 lbs (90 kg).

Using metric units:

  • Height in meters: 175 ÷ 100 = 1.75 m
  • Height squared: 1.75 × 1.75 = 3.0625 m²
  • BMI: 90 ÷ 3.0625 = 29.4

Using imperial units:

  • Height in inches: (5 × 12) + 9 = 69 in
  • Height squared: 69 × 69 = 4,761 in²
  • BMI: 703 × 198 ÷ 4,761 = 139,194 ÷ 4,761 = 29.2 (rounding differences)

Category: Overweight (BMI 25–29.9).

Healthy weight range for 5'9":

  • Lower bound (BMI 18.5): 18.5 × 3.0625 = 56.7 kg ≈ 125 lbs
  • Upper bound (BMI 24.9): 24.9 × 3.0625 = 76.3 kg ≈ 168 lbs

To reach the upper end of normal: lose about 30 lbs (from 198 to 168). At a healthy rate of 1–2 lbs per week, that's a 15–30 week journey with a moderate caloric deficit of 500–1,000 calories per day.

"/> Glossary

BMI (Body Mass Index)
A screening measure of body fatness based on height and weight. Useful at the population level, less precise for individuals with high muscle mass.
BMI Prime
Your BMI divided by 24.9 (the upper limit of normal). A value below 1.0 is in the healthy range; above 1.0 is overweight or obese.
Healthy Weight Range
The body weight that corresponds to a BMI between 18.5 and 24.9 for a given height.
Visceral Fat
Fat stored deep inside the abdomen around organs. More metabolically dangerous than subcutaneous fat and not captured by BMI.
Sarcopenic Obesity
High body fat paired with low muscle mass—common in older adults with "normal" BMI but elevated metabolic risk.
Waist-to-Height Ratio
A simple alternative to BMI: keep waist circumference under half your height. Often predicts cardiovascular risk better than BMI.
FAQ

Frequently asked questions

Quick answers to the most common questions about bmi calculator.

What is BMI and how is it calculated?
Body Mass Index (BMI) estimates body fat based on height and weight. The formula is weight (kg) / height (m)², or 703 × weight (lbs) / height (in)². The result places you in a category: underweight (<18.5), normal (18.5–24.9), overweight (25–29.9), or obese (30+).
Is BMI accurate for everyone?
No. BMI doesn't distinguish muscle from fat, so very muscular athletes may register as "overweight" or "obese" despite being lean. It also doesn't account for body fat distribution, age-related muscle loss, or differences across ethnic groups. Use BMI as a screening tool, not a definitive health measure.
What is a healthy BMI range?
For most adults, a BMI between 18.5 and 24.9 is considered healthy. Some research suggests the lowest mortality risk is in the 22–25 range. The World Health Organization defines overweight as 25+ and obesity as 30+, though some Asian populations use lower cutoffs (23+ for overweight) due to higher health risks at lower BMIs.
Should I worry about a high BMI if I exercise regularly?
If you're physically active, eat well, and have good metabolic markers (blood pressure, cholesterol, blood sugar), a slightly elevated BMI may not be a major concern. Cardiovascular fitness is a stronger predictor of mortality than BMI alone. However, BMIs above 30 should prompt a conversation with your doctor.
How does BMI differ for children and teens?
For children and teens (2–19 years), BMI is calculated the same way but interpreted using age- and sex-specific percentile charts rather than fixed categories. A BMI at the 85th–94th percentile is "overweight," and 95th percentile or above is "obese." Always consult a pediatrician for child BMI interpretation.

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This calculator is provided for informational and educational purposes only and does not constitute financial, legal, tax, or professional advice. Results are estimates based on the inputs you provide and standard assumptions. Actual figures may vary. Please consult a qualified professional before making financial decisions. Read our full disclaimer.