BCBetter Calculators

BMI Calculator

Calculate your Body Mass Index (BMI) and see where you fall on the standard BMI scale.

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Enter your values and click Calculate

How It Works

BMI is calculated from height and weight using one of two equivalent formulas depending on the selected unit system. For metric inputs: BMI = Weight (kg) ÷ Height (m)². This divides your weight in kilograms by the square of your height in meters. For example, 75 kg at 1.75 m gives BMI = 75 ÷ (1.75²) = 75 ÷ 3.0625 = 24.5. For imperial inputs (lbs and feet/inches): BMI = (Weight in lbs ÷ Height in inches²) × 703. The constant 703 is a unit-conversion factor that produces the same numerical result as the metric formula when US units are used. A person weighing 170 lbs at 5 feet 10 inches (70 total inches) has BMI = (170 ÷ 4900) × 703 = 24.4. The calculator classifies the result into four WHO-defined categories: Underweight (below 18.5), Normal weight (18.5–24.9), Overweight (25.0–29.9), and Obese (30.0 and above). It also computes the healthy weight range for your specific height by reversing the formula — taking the BMI boundaries of 18.5 and 24.9, multiplying each by height in meters squared, then converting the result back to your preferred weight unit. This gives you a concrete minimum and maximum weight target rather than a single abstract BMI score. Both the BMI score and healthy weight range update dynamically as inputs change.

Examples

170 lbs, 5'10" — Imperial
A common height and weight combination for adult males in the US, calculated in imperial units.
Result: BMI of 24.4 — Normal weight.
80 kg, 175 cm — Metric
A standard metric calculation for a slightly above-average weight adult.
Result: BMI of 26.1 — Overweight.
250 lbs, 5'8" — Obese range
A higher weight example illustrating the Obese classification and healthy weight target.
Result: BMI of 38.0 — Obese. Healthy weight range for this height is approximately 122–164 lbs.

Frequently Asked Questions

Is BMI accurate?
BMI is a useful population-level screening tool but has well-documented limitations at the individual level. It cannot distinguish between muscle mass and body fat, so athletes with high muscle density often register as Overweight or Obese despite low body fat percentage. It also does not account for age, sex, or ethnicity — all of which affect how body fat is distributed and what level of BMI correlates with metabolic risk. BMI is best used as a starting point for a health conversation, not as a standalone diagnostic.
What is a healthy BMI range?
The World Health Organization defines the healthy BMI range as 18.5 to 24.9. However, research suggests optimal ranges may shift with age — older adults may benefit from a slightly higher BMI — and evidence indicates that metabolic risk thresholds differ across ethnic groups. Several Asian health organizations recommend lower cut-off points, around 23.0 for overweight, due to higher risk of metabolic disease at BMI levels that appear normal by the standard WHO scale.
What is a BMI of 30?
A BMI of 30.0 marks the threshold for Obese Class I, which spans 30.0–34.9. Class II Obesity begins at 35.0, and Class III (sometimes called severe or morbid obesity) begins at 40.0. A BMI of 30 is associated with elevated risk of type 2 diabetes, hypertension, sleep apnea, and cardiovascular disease, though individual risk depends heavily on factors including physical activity level, diet, fat distribution, and genetics.

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