BMI Calculator
Calculate your Body Mass Index (BMI) instantly using height and weight in metric or imperial units. See your BMI category, healthy weight range, BMI Prime, and a full explanation of what your result means and its limitations.
Your BMI Result
How to Use This Tool
- Choose your unit system — Metric (kg/cm) or Imperial (lb/ft & in).
- Enter your weight in kilograms (metric) or pounds (imperial).
- Enter your height in centimeters (metric) or feet and inches (imperial).
- View your BMI score, category (Underweight, Normal, Overweight, or Obese), healthy weight range, and BMI Prime, calculated instantly as you type.
- Compare your BMI against the standard WHO categories shown on the color-coded scale bar.
Formula & How It Works
BMI Formula (Metric)
BMI = Weight (kg) ÷ Height (m)²Weight in kilograms divided by height in meters, squared. This is the formula the calculator uses internally after converting imperial inputs to metric.
BMI Formula (Imperial)
BMI = (Weight (lb) ÷ Height (in)²) × 703The imperial version of the same formula, scaled by 703 so it produces the identical result as the metric calculation.
Healthy Weight Range
Low = 18.5 × Height (m)², High = 24.9 × Height (m)²The calculator multiplies the Normal BMI boundaries (18.5 and 24.9) by your height squared to show the weight range considered normal for your height.
BMI Prime
BMI Prime = BMI ÷ 25Your BMI divided by 25 (the upper bound of Normal weight). A value above 1.0 means you are above the Normal range; below 1.0 means you are within or under it.
Practical Examples & Common Use Cases
Metric example — 80 kg, 180 cm adult
Height in meters is 1.80, so height squared is 3.24. BMI = 80 ÷ 3.24 = 24.7, which falls in the Normal Weight category (18.5–24.9). The healthy weight range for 180 cm is about 59.9–80.7 kg, and BMI Prime is 24.7 ÷ 25 = 0.99.
Metric example — 95 kg, 170 cm adult
Height in meters is 1.70, so height squared is 2.89. BMI = 95 ÷ 2.89 = 32.9, which falls in the Obese (Class I) category (30.0–34.9). BMI Prime is 32.9 ÷ 25 = 1.32, meaning this person is 32% above the upper limit of Normal weight.
Imperial example — 154 lb, 5 ft 9 in adult
Height in inches is (5 × 12) + 9 = 69 in. BMI = (154 ÷ 69²) × 703 = (154 ÷ 4,761) × 703 = 22.7, which falls in the Normal Weight category. This matches the metric calculation for the equivalent 70 kg, 175 cm person.
Frequently Asked Questions
According to WHO standards, a BMI between 18.5 and 24.9 is considered Normal Weight for adults. However, optimal healthy weight varies by age, sex, ethnicity, and body composition. A BMI in the normal range is a useful indicator but not a complete measure of health.
No. BMI can significantly overestimate body fat in muscular or athletic individuals because muscle is denser than fat. A bodybuilder or competitive athlete may register as "Overweight" or "Obese" by BMI while having very low body fat. For athletes, body fat percentage is a more meaningful measure.
BMI Prime is your BMI divided by 25, the upper limit of the Normal range. A BMI Prime of 1.0 means you are exactly at the normal/overweight boundary. Below 1.0 is normal or underweight; above 1.0 is overweight. A BMI Prime of 1.2, for example, means you are 20% above the upper normal limit.
No. Children and teenagers (ages 2–19) use a different BMI scale that accounts for age and sex because body composition changes significantly during growth. For children, BMI is expressed as a percentile compared to peers of the same age and sex. This calculator is designed for adults 18 and older.
BMI does not measure fitness, cardiovascular health, nutrition, or where body fat is distributed. A person can have a normal BMI but carry dangerous levels of visceral (abdominal) fat, have poor metabolic health, or low muscle mass — all of which affect wellbeing. BMI is a starting point, not a complete health assessment.
A high BMI is one signal worth discussing with a healthcare provider, who can do a more complete assessment including blood pressure, blood sugar, cholesterol, and other markers. Do not make significant dietary or medical decisions based solely on your BMI result.
BMI is an indirect estimate calculated only from height and weight. Body fat percentage directly measures how much of your body mass is fat versus lean tissue (muscle, bone, water). Body fat percentage is more informative but requires additional measurement methods such as DEXA scans, hydrostatic weighing, or skinfold calipers.
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