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Health & FitnessReviewed Methodology

BMI Calculator

This BMI calculator lets you check your body mass index quickly using either metric or US units. Enter your height and weight, and the tool will return your BMI score along with the standard category it falls into. BMI is commonly used as a simple screening tool to help identify weight categories that may be associated with health considerations.

Health & Fitness

Quick answer

BMI is calculated from your height and weight. It does not measure body fat directly.

Using kilograms and centimeters.

kg
cm

What this tells you

  • •BMI is calculated from your height and weight. It does not measure body fat directly.
  • •The standard categories are underweight, normal weight, overweight, and obesity.
  • •BMI is a screening estimate, not a diagnosis. It works best as a starting reference.

How to Use

  1. 1Choose your preferred unit system: Metric (kg and cm) or US (lb, feet, and inches).
  2. 2Enter your weight.
  3. 3Enter your height.
  4. 4Review your BMI score, category, and the short interpretation below.

How It Works

Formula

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

BMI divides your weight by the square of your height to produce a single number. In the metric formula, height must be in meters. In the US formula, the constant 703 converts pounds and inches into the same scale. The resulting number is then compared to standard ranges to assign a category.

Calculation note: values are processed in the order shown above, using the current input units.

Worked Examples

Example 1: Metric — Normal Weight

Weight70 kg
Height175 cm
ResultBMI 22.9 — Normal weight

Height in meters = 1.75. BMI = 70 ÷ (1.75 × 1.75) = 70 ÷ 3.0625 = 22.9. This falls within the normal weight range (18.5–24.9).

Example 2: US — Overweight

Weight200 lb
Height5 ft 8 in
ResultBMI 30.4 — Obesity

Height in inches = (5 × 12) + 8 = 68 inches. BMI = 703 × 200 ÷ (68 × 68) = 140,600 ÷ 4,624 = 30.4. This falls in the obesity range (30+).

Common mistakes

  • Entering height in centimeters when the calculator is set to US units, or vice versa
  • Confusing total height in inches with the inches portion only when using feet and inches
  • Treating BMI as a precise measure of body fat rather than a general screening number
  • Applying adult BMI categories to children or adolescents, who use different charts
  • Ignoring that athletes with high muscle mass may score high without excess fat

Limitations

BMI is a general screening estimate. It does not measure body fat directly and may not reflect health accurately for athletes, children, pregnant people, or older adults.

Frequently Asked Questions

BMI stands for body mass index. It is a number calculated from your height and weight that is used as a simple screening tool for weight categories.
A BMI between 18.5 and 24.9 is considered normal weight for adults. However, BMI is only one factor and does not capture the full picture of health.
No. BMI may overestimate body fat in muscular individuals and underestimate it in older adults or people with low muscle mass. It is best used as a starting reference.
In metric, BMI equals weight in kilograms divided by height in meters squared. In US units, BMI equals 703 times weight in pounds divided by height in inches squared.
This calculator uses adult BMI categories. Children and teens require age- and sex-specific BMI percentile charts, which this tool does not provide.
No. BMI estimates a weight-to-height ratio. It does not distinguish between fat, muscle, or bone mass.
Consider speaking with a healthcare provider. BMI is a starting point, not a final assessment. Your provider can consider other factors like diet, activity, and family history.

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