BMI Calculator

This BMI Calculator helps you estimate your Body Mass Index using your height and weight. It's a quick way to understand whether your weight is generally low, typical, or high for your height. This tool is useful for adults who want a simple screening number to track changes over time, set fitness goals, or start a health conversation. Your result is a single BMI value, along with a general category so you can interpret it more easily. Keep in mind that BMI is a guide, not a diagnosis, and it does not measure body fat directly.

How to Use This Calculator

1. Choose your measurement system (Metric or Imperial), if the tool offers both.
2. Enter your height (cm or ft/in).
3. Enter your weight (kg or lb).
4. Click Calculate to get your BMI.
5. Review the BMI number and the category shown with it.
6. Re-check your entries if the result looks surprising.

What This Calculator Measures

This calculator measures Body Mass Index (BMI).

• BMI is a number that compares your weight to your height.
• It is commonly used as a screening tool to group weight status into broad categories.
• It works best for most adults, but it does not consider everything about your body.

Key terms (simple definitions):

• Height: How tall you are.
• Weight: How much you weigh.
• BMI value: The final number calculated from height and weight.
• BMI category: A general label (like underweight or overweight) based on the BMI value.

Formula or Logic

BMI is calculated by dividing your weight by your height squared.

• In metric, it uses kilograms and meters: weight (kg) compared to height (m × m).
• In imperial, it uses pounds and inches with a standard conversion factor.

You don't need to do the math yourself. The calculator handles it and shows your BMI instantly.

Example Calculations

Example 1 (Metric)

• Height: 170 cm (1.70 m)
• Weight: 65 kg
• BMI: 65 ÷ (1.70 × 1.70) = 22.5

Example 2 (Metric)

• Height: 160 cm (1.60 m)
• Weight: 80 kg
• BMI: 80 ÷ (1.60 × 1.60) = 31.2

Example 3 (Imperial)

• Height: 5 ft 6 in (66 in)
• Weight: 150 lb
• BMI: (150 × 703) ÷ (66 × 66) = 24.2

The factor 703 converts the result from lb/in² to the standard kg/m² scale used in BMI classification.

Understanding Your Results

Your BMI number is commonly interpreted using these adult categories, as defined by the CDC (Centers for Disease Control and Prevention):

• Underweight: below 18.5
• Healthy weight: 18.5 to 24.9
• Overweight: 25.0 to 29.9
• Obesity: 30.0 and above

Important limitations to keep in mind:

• BMI does not measure body fat directly and does not tell you where fat is stored in the body.
• Muscular people may have a higher BMI despite low body fat, because muscle is denser than fat — a limitation the CDC acknowledges in its BMI guidance.
• For children and teens, BMI is interpreted differently (using age- and sex-specific growth charts) and should not be compared to adult categories.
• Ethnic and population differences: The World Health Organization (WHO) and some national health bodies note that individuals of Asian descent may have higher health risks at lower BMI thresholds. Some guidelines use lower cut-offs (e.g., overweight at BMI ≥ 23 for certain Asian populations). If this applies to you, discuss appropriate thresholds with your healthcare provider.
• For a complete health assessment, consult a qualified healthcare professional. BMI is a population-level screening tool, not a clinical diagnosis for any individual.

Why BMI Has Limits as a Health Measure

BMI was originally developed in the 1830s by Belgian statistician Adolphe Quetelet as a statistical tool for studying populations — not for assessing individual health. Despite this, it became widely adopted in clinical settings because of its simplicity.

Research consistently shows BMI cannot distinguish between fat mass and lean mass. An elite athlete may register as "overweight" by BMI while having very low body fat. Conversely, a person with normal BMI may carry significant visceral (abdominal) fat, which carries its own metabolic risk. For this reason, many clinicians pair BMI with waist circumference, waist-to-hip ratio, or body fat percentage measurements for a fuller picture of health risk.

Common Mistakes to Avoid

• Mixing units (entering pounds in the kg field, or inches in the cm field).
• Forgetting to include inches after feet (for example, entering only "5").
• Using shoes-on height or guessing height from memory.
• Using a weight from a different time of day (weight can fluctuate).
• Comparing your BMI directly with someone of a very different body type.
• Treating BMI as a diagnosis instead of a screening number.
• Ignoring other health factors like waist size, activity level, or medical history.

For a more complete picture of your health, consider pairing your BMI result with waist circumference measurement (the CDC considers waist circumference above 35 inches for women and 40 inches for men an additional health risk indicator) and a conversation with your doctor about your individual risk factors.

Frequently Asked Questions

What is a healthy BMI for adults?

According to the CDC, a BMI between 18.5 and 24.9 is considered a healthy weight range for most adults. However, "healthy" depends on many factors beyond BMI — including age, sex, muscle mass, ethnicity, and where body fat is distributed. Always discuss your results with a healthcare provider.

Is BMI the same for men and women?

The standard BMI calculation and categories (underweight, healthy, overweight, obese) are the same for adult men and women. However, women typically have a higher percentage of body fat at the same BMI compared to men, because men tend to carry more muscle mass. This is a known limitation of BMI as a single metric.

Can BMI be used for children?

Not with adult categories. For children and teens aged 2–19, the CDC uses BMI-for-age percentiles that account for age and sex. A child's BMI is interpreted using growth charts, not the adult thresholds of 18.5–24.9. Use a paediatric BMI calculator designed for this purpose.

Why is my BMI high if I exercise regularly?

Dense muscle tissue weighs more than fat tissue for the same volume. A trained athlete may have a BMI in the "overweight" range while carrying very little body fat. For athletes and highly active individuals, body fat percentage measurement (via DEXA scan, hydrostatic weighing, or skinfold calipers) is a more meaningful health metric than BMI.

Does BMI account for age?

The standard adult BMI formula does not adjust for age directly. However, body composition changes with age — older adults tend to have more body fat at the same BMI compared to younger adults, and some health risks associated with higher BMI are more pronounced at older ages. Discuss age-specific considerations with your doctor.