This BMI calculator finds your body mass index — a screening number that relates your weight to your height — and tells you which CDC weight category you fall into, along with the healthy weight range for someone your height. BMI is used worldwide by doctors, insurers, and public-health agencies because it is quick, free, and correlates reasonably well with body fatness across large populations.
Enter your height and weight in US or metric units to get your BMI instantly. Keep in mind that BMI is a screening tool, not a diagnosis: it cannot distinguish muscle from fat, so pair it with other measures like waist circumference or body fat percentage.
The BMI Formula
BMI is defined as weight in kilograms divided by height in meters squared:
BMI = weight (kg) ÷ height² (m²)
With US units, the equivalent formula multiplies by a conversion factor of 703:
BMI = 703 × weight (lbs) ÷ height² (inches²)
Both versions give the same result. Because height is squared in the denominator, small height differences change BMI substantially — a 150-lb person has a BMI of 25.7 at 5'4" but only 20.3 at 6'0". The healthy weight range shown by this calculator simply inverts the formula: it multiplies your height in meters squared by 18.5 and 24.9, the boundaries of the normal category, then converts back to pounds if you chose US units.
CDC BMI Categories and BMI's Limitations
The CDC defines four standard categories for adults aged 20 and older:
- Underweight: BMI below 18.5
- Normal (healthy) weight: 18.5 – 24.9
- Overweight: 25 – 29.9
- Obese: 30 and above (Class 1: 30–34.9, Class 2: 35–39.9, Class 3: 40+)
BMI has well-known blind spots. Muscular athletes often score as "overweight" because muscle is denser than fat — many NFL players have BMIs over 30 with low body fat. Older adults can hold a "normal" BMI while carrying too little muscle. Some research also suggests risk thresholds differ by ethnicity; for example, health risks may begin at a BMI of 23 in some Asian populations. Use BMI as a first screen, not a verdict.
Example: 5'10" and 165 lbs
Convert to metric: 70 inches × 2.54 = 177.8 cm = 1.778 m, and 165 lbs ÷ 2.2046 = 74.8 kg.
BMI = 74.8 ÷ (1.778 × 1.778) = 74.8 ÷ 3.161 = 23.7 kg/m²
A BMI of 23.7 falls in the normal weight category (18.5 – 24.9). The healthy weight range for this height is 18.5 × 3.161 = 58.5 kg (129 lbs) up to 24.9 × 3.161 = 78.7 kg (174 lbs). Using the US formula gives the same answer: 703 × 165 ÷ 70² = 703 × 165 ÷ 4,900 = 23.7.
Frequently Asked Questions
What is a healthy BMI?
A healthy BMI for adults is 18.5 to 24.9 kg/m², according to the CDC and World Health Organization. Below 18.5 is underweight, 25 to 29.9 is overweight, and 30 or above is obese. For a 5'10" adult, the healthy range corresponds to roughly 129–174 pounds.
How do I calculate BMI by hand?
Divide your weight in kilograms by your height in meters squared. In US units, multiply your weight in pounds by 703, then divide by your height in inches squared. Example: 165 lbs at 70 inches is 703 × 165 ÷ 4,900 = 23.7.
Is BMI accurate for athletes?
No — BMI often overestimates fatness in muscular people because muscle weighs more than fat per unit of volume. A lean bodybuilder can register as overweight or obese by BMI alone. Athletes should rely on body fat percentage, waist circumference, or DEXA scans for a more accurate picture.
Does BMI work the same for men and women?
The formula and adult categories are identical for both sexes, even though women naturally carry more body fat than men at the same BMI. That is one of its accepted limitations as a population-level screening tool. For children and teens aged 2–19, BMI is instead evaluated with age- and sex-specific percentile charts.
What should I do if my BMI is in the overweight or obese range?
Treat it as a prompt to look deeper, not a diagnosis. Check your waist circumference (over 40 inches for men or 35 inches for women adds risk), and talk with a healthcare provider. A modest 5–10% weight loss measurably improves blood pressure, blood sugar, and cholesterol.