BMI Calculator
Find your body mass index and what it means. Enter your height and weight in US or metric units to see your BMI on a visual WHO category gauge, your healthy weight range in both pounds and kilograms, and exactly how far you are from it.
24.4 BMI — Healthy weight
Healthy weight for your height: 125.3 lb – 168.6 lb
Within the healthy weight range. BMI prime: 0.97 (1.00 = top of healthy range).
Categories follow WHO/CDC adult BMI ranges. BMI is a screening tool, not a diagnosis, and doesn’t distinguish muscle from fat. How we calculate →
How BMI is calculated
Body mass index compares your weight to your height. In metric units it's BMI = weight (kg) ÷ height (m)²; in US units, BMI = 703 × weight (lb) ÷ height (in)². For example, someone 5'9" (1.75 m) weighing 165 lb (75 kg) has a BMI of about 24.4. The calculator above does the conversion for you in either unit system — just enter your height and weight.
BMI is a quick screening number, not a body-fat measurement. It's useful at a population level and as a personal starting point, but it doesn't account for muscle, frame or fat distribution.
BMI categories (WHO)
The World Health Organization classifies adult BMI into four ranges: underweight below 18.5, healthy weight 18.5–24.9, overweight 25–29.9, and obesity 30 and above. The colored gauge above marks where your BMI falls and how close you are to the next band. These thresholds are the same ones used by the CDC and NHLBI for adults aged 20 and over.
Your healthy weight range
Because the healthy band is a BMI range, it maps to a weight range for your height. The calculator shows your healthy range in both pounds and kilograms — for a 5'9" adult that's roughly 125–169 lb (56–77 kg) — and tells you how far above or below it you are. That target-weight figure is what most BMI tools leave out, and it's far more actionable than the index alone.
What BMI doesn't tell you
BMI can misclassify people because it only uses height and weight. A muscular athlete can have a 'high' BMI with very low body fat, while an older adult who has lost muscle can have a 'normal' BMI with too much fat. It also doesn't show where fat sits — waist measurement and waist-to-height ratio capture abdominal fat, a better marker of health risk. Treat BMI as one screening signal, not a verdict.
BMI for children and teens
For anyone under 20, BMI is interpreted differently: it's compared against CDC growth charts for the child's age and sex to give a percentile, because healthy body composition changes as kids grow. A teen's raw BMI number isn't matched to the adult 18.5–25 bands. This calculator is built for adults (20+); for a child or teen, use the CDC's BMI-for-age percentile calculator and talk to a pediatrician.
Beyond BMI: prime and waist-to-height
BMI prime is your BMI divided by 25 (the top of the healthy range): under 1.00 is within range, over 1.00 is above it — a quick way to see how far off you are as a ratio. Pairing BMI with waist-to-height ratio (keep your waist under half your height) gives a fuller picture than either number alone, especially for people whose BMI sits near a boundary.
Frequently asked questions
How do I calculate my BMI manually?
In metric, divide your weight in kilograms by your height in metres squared (kg ÷ m²). In US units, multiply your weight in pounds by 703 and divide by your height in inches squared. For 165 lb at 69 inches: 703 × 165 ÷ 69² ≈ 24.4. The calculator above does it in either unit.
What is a healthy BMI?
For adults, the WHO healthy range is a BMI of 18.5 to 24.9. Below 18.5 is underweight, 25–29.9 is overweight, and 30 or above is obesity. The calculator also shows the actual weight range for your height that keeps you in the healthy band.
What BMI is considered overweight or obese?
A BMI of 25 to 29.9 is classified as overweight and a BMI of 30 or higher as obesity, under WHO and CDC definitions for adults. The gauge above shows which band your BMI falls into and how close you are to the next one.
Is BMI accurate for muscular people or athletes?
Not always. BMI uses only height and weight, so a muscular athlete can register as 'overweight' despite low body fat, because muscle weighs more than fat. For very muscular or very lean people, body-fat percentage or waist measurement is a better indicator than BMI.
Why is BMI sometimes misleading?
BMI doesn't distinguish muscle from fat or show where fat is stored, and it can misjudge older adults, athletes and some ethnic groups. It's a useful population screening tool and a personal starting point, but it shouldn't be the only measure — pair it with waist-to-height ratio and a clinician's input.
What is the BMI range for children and teens?
For under-20s, BMI is read as a percentile against CDC growth charts for age and sex, not the adult 18.5–25 bands, because healthy body composition changes with growth. Use the CDC's BMI-for-age calculator for children and consult a pediatrician.
How much should I weigh for my height?
Your healthy weight is the range that puts your BMI between 18.5 and 24.9. For a 5'9" adult that's about 125–169 lb; for 5'4" it's about 108–145 lb. Enter your height above and the calculator shows your range in both pounds and kilograms.
What is BMI prime?
BMI prime is your BMI divided by 25, the upper limit of the healthy range. A value under 1.00 means you're within the healthy range; 1.20, for instance, means your BMI is 20% above the healthy ceiling. It's a quick ratio for seeing how far off you are.
Researched & verified by the Calcuris Data & Research Team. How we build and check our tools →