BMI Calculator

Calculate your BMI in imperial or metric units, see your WHO weight category, and find the healthy weight range for your height.

By Drew Budwin · Last updated July 2026 · Methodology

Whole feet (e.g. 5)

Remaining inches (0–11)

Your weight in pounds.

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How We Calculate This

How BMI Is Calculated

BMI is a ratio of your weight to the square of your height. The metric formula divides weight in kilograms by height in meters squared. When you enter imperial units, the calculator uses the standard conversion so an imperial BMI matches the metric result exactly.

Metric: BMI = weight (kg) ÷ height (m)²
Imperial: BMI = 703 × weight (lb) ÷ height (in)²

Both formulas are the standard defined by the NHLBI and CDC. The factor of 703 converts pounds and inches to the metric scale, so entering 160 lb at 70 inches gives the same BMI as entering 72.6 kg at 1.78 m.

What the WHO Categories Mean

The World Health Organization sorts adult BMI into four main bands, applied the same way to men and women:

  • Underweight: below 18.5
  • Normal weight: 18.5–24.9
  • Overweight: 25.0–29.9
  • Obesity: 30.0 and above

These cut-points are population thresholds set by the WHO to flag health risk. They describe where you sit relative to the adult population, not a diagnosis of your individual health.

Where BMI Falls Short

BMI is a screening number, not a body-fat measurement. The CDC states that BMI does not directly measure body fat, and research shows it correlates with body fat only at the population level, not for every individual.

  • Muscle counts as weight. A muscular athlete can register as overweight or obese while carrying little fat.
  • Sex differences. Women typically carry more body fat than men at the same BMI, yet the formula uses one equation for both.
  • Age shifts composition. Older adults tend to lose muscle and gain fat, so the same BMI can mean more fat at 65 than at 25.

Read BMI alongside waist circumference, body composition, and your medical history. Use it to start a conversation with a clinician, not to end one.

This calculator is for informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. For personal health decisions, consult a qualified healthcare provider. About Adult BMI — CDC

BMI Calculator Formula

BMI is calculated from height and weight:

BMI = weight (kg) ÷ height² (m²)

For imperial inputs, convert first:

height (m) = total inches × 0.0254 | weight (kg) = pounds × 0.453592

How to Use This Calculator

  1. Choose your unit system: Imperial (feet, inches, pounds) or Metric (centimeters, kilograms).
  2. Enter your height and weight using the fields that appear.
  3. Click Calculate BMI to see your BMI, category, and healthy weight range.

Frequently Asked Questions

Is this BMI result medical advice?

No. This calculator is for informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. BMI is a screening tool, not a diagnosis. Consult a qualified healthcare provider to interpret your result alongside other measures such as waist circumference, body composition, and medical history.

What is a healthy BMI?

According to the World Health Organization, a BMI of 18.5–24.9 is considered normal weight. Below 18.5 is underweight, 25.0–29.9 is overweight, and 30.0 or above is classified as obese.

Is BMI accurate for everyone?

BMI is a useful screening tool, but it has limitations. The CDC notes that BMI does not directly measure body fat and uses the same formula for all adults regardless of sex, even though women typically carry more body fat than men at the same BMI. It also does not distinguish between muscle and fat, so athletes with high muscle mass may have an elevated BMI that does not reflect excess body fat. For a more complete picture of your energy needs, try the BMR calculator to estimate your daily calorie requirements. Use BMI as a general guideline rather than a definitive health assessment.

How do I calculate BMI in imperial units?

Convert your height to total inches (feet × 12 + remaining inches), then to meters by multiplying by 0.0254. Convert your weight from pounds to kilograms by multiplying by 0.453592. Then divide weight (kg) by height (m) squared.

What is the healthy weight range for my height?

The healthy weight range corresponds to a BMI of 18.5–24.9 (Normal weight). This calculator shows your personal healthy weight range based on the height you enter.

What are the full WHO BMI classifications?

The World Health Organization classifies adult BMI (age 20+) into the following categories, used for both men and women:

WHO adult BMI classification bands.
ClassificationBMI range (kg/m²)
Severe Thinness< 16
Moderate Thinness16–17
Mild Thinness17–18.5
Normal18.5–24.9
Overweight25.0–29.9
Obese Class I30.0–34.9
Obese Class II35.0–39.9
Obese Class III> 40

Does BMI apply to children and teenagers?

BMI is calculated the same way for children, but the interpretation differs. For ages 2–19, BMI is plotted on age- and sex-specific growth charts and expressed as a percentile. This calculator is designed for adults (age 20+).

Further Reading

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