What BMI actually tells you
Body mass index (BMI) is a screening number that compares your weight to your height. It was devised in the 1830s by the Belgian statistician Adolphe Quetelet — clinicians still call it the Quetelet index — and the World Health Organization later adopted it as the standard way to classify adult weight status, because it turns two easy measurements into a single comparable figure.
What BMI is not: a body-fat test or a diagnosis. It cannot see how much of your weight is muscle, bone or fat, so treat it as a first look, not a verdict.
How to use the calculator
- Pick your units: pounds with feet and inches, or kilograms with centimeters.
- Enter your weight.
- Enter your height.
- Read the result: your BMI to one decimal place, your WHO category highlighted in the table, and the weight range considered healthy for your height.
Everything runs in your browser — nothing you type is sent or stored anywhere.
The formula (metric and imperial)
The metric definition is BMI = weight ÷ height², with weight in kilograms and height in meters. If you work in pounds and inches, the equivalent shortcut is BMI = 703 × pounds ÷ inches² — the 703 factor simply converts the units.
Worked example
Say you weigh 180 lb and stand 5 ft 10 in tall, which is 70 inches. Square the height: 70 × 70 = 4,900. Then BMI = 703 × 180 ÷ 4,900 = 126,540 ÷ 4,900 = 25.8, which lands in the overweight category (25 to 29.9), just above the normal range. The healthy weight range for 5 ft 10 in works out to roughly 129 to 174 lb (about 58.5 to 78.7 kg), so this person would reach the top of the normal range at around 174 lb.
Healthy weight by height
Weight ranges that correspond to a BMI between 18.5 and 24.9 (adults, rounded to the nearest pound):
| Height | Healthy weight range |
|---|---|
| 5 ft 0 in | 95 – 128 lb |
| 5 ft 2 in | 101 – 136 lb |
| 5 ft 4 in | 108 – 145 lb |
| 5 ft 6 in | 115 – 154 lb |
| 5 ft 8 in | 122 – 164 lb |
| 5 ft 10 in | 129 – 174 lb |
| 6 ft 0 in | 136 – 184 lb |
| 6 ft 2 in | 144 – 194 lb |
Where BMI falls short
These limitations are real and well documented — keep them in mind when reading your number:
- Muscle counts as weight. A rugby player or weightlifter can score “overweight” or even “obese” while carrying very little fat.
- Older adults. Muscle mass declines with age, so a “normal” BMI can hide excess body fat in seniors.
- Pregnancy. Standard BMI categories do not apply during pregnancy.
- Children and teens. Under 18, BMI is read against age- and sex-specific percentiles (growth charts), not these fixed cutoffs — this calculator is for adults only.
- Fat location is invisible to it. Abdominal fat carries the highest cardiometabolic risk, and BMI cannot tell where your weight sits.
What to do with your result
Use it as a conversation starter. If your BMI falls outside the normal range — or sits inside it but your body composition tells a different story — measure your waist, look honestly at sleep, diet and activity, and bring the numbers to a doctor or registered dietitian. This tool is informational only and is not a substitute for professional medical advice.
Frequently asked questions
How reliable is BMI?
At the population level, quite reliable — it tracks health risk well across large groups. For an individual it is only a rough guide, because it ignores muscle mass, fat distribution, age and sex. That is exactly why clinicians pair it with other measurements instead of using it alone.
Can I use this calculator for my child?
No. For anyone under 18, BMI must be plotted on growth charts and interpreted as a percentile for their age and sex — the same number can be perfectly fine at one age and concerning at another. Ask your pediatrician to assess it.
What is better than BMI?
Waist circumference and the waist-to-height ratio pick up abdominal fat, the riskiest kind. Body-composition tests (bioelectrical impedance scales, DEXA scans) measure fat percentage directly. None of these replaces a medical evaluation, but each fills a gap BMI leaves open.