How to Use This Calculator
- 1
Pick your unit system
US units (feet, inches, and pounds) are selected by default; tap Metric to switch to centimeters and kilograms. Your entries are kept when you toggle back and forth.
- 2
Enter your height
In US mode, fill in feet and inches separately — 5 and 10 for someone five-foot-ten. Height gets squared in the math, so even an inch of error noticeably shifts the result.
- 3
Enter your weight
Use a recent weigh-in, ideally taken first thing in the morning. A pound or two either way only moves BMI by a few tenths of a point, so don't obsess over daily fluctuations.
- 4
Interpret the result
The big number is your BMI, the colored chip names your category, and the marker on the scale bar shows where you sit between 15 and 40. Compare your current weight against the healthy range listed for your height.
How It Works
Body Mass Index scales your weight by the square of your height. It was designed as a fast screening number for large populations, and both unit systems produce the same value:
For adults 20 and older, the WHO and CDC define four ranges: below 18.5 is underweight, 18.5–24.9 is normal weight, 25.0–29.9 is overweight, and 30.0 or above is obesity. Because height is fixed, each range also maps to a weight band — that's the “healthy weight for your height” figure the calculator shows.
Worked example
Take someone who stands 5 ft 10 in (70 inches) and weighs 170 lb.
BMI = 703 × 170 ÷ 702 = 119,510 ÷ 4,900 ≈ 24.4 — inside the normal range, right near its upper edge.
At that height, the 18.5–24.9 band corresponds to roughly 129–174 lb, so this person has only a few pounds of headroom before crossing into the overweight category.
Frequently Asked Questions
What is a healthy BMI for adults?
For adults 20 and older, a BMI between 18.5 and 24.9 counts as normal weight under both WHO and CDC guidelines. Below 18.5 is underweight, 25.0–29.9 is overweight, and 30.0 or above is classified as obesity. In practical terms, a person standing 5 ft 10 in falls in the normal range anywhere from about 129 to 174 pounds — a surprisingly wide 45-pound window.
Is BMI accurate for muscular people and athletes?
Not very. BMI cannot tell muscle from fat, and muscle is considerably denser, so lean, well-trained people often score as overweight. Plenty of professional athletes carry single-digit body fat yet post BMIs above 28. If you strength train seriously, treat a high reading with skepticism and look at waist circumference, body fat percentage, or a DEXA scan instead.
What's the difference between BMI and body fat percentage?
BMI is a quick ratio computed from nothing but height and weight; body fat percentage measures what that weight is actually made of. Healthy body fat typically runs about 10–20% for men and 18–28% for women. Two people with an identical BMI of 27 could be a lean lifter and a sedentary person carrying excess visceral fat — only body composition testing tells them apart.
Do the BMI cutoffs change with age or sex?
For adults 20 and over, the same cutoffs apply to everyone — that simplicity is both BMI's appeal and its weakness. Women naturally carry more body fat than men at the same BMI, and some research suggests adults over 65 fare best at slightly higher values, around 25–27. Treat the categories as a screening guide, not a diagnosis.
My BMI is high — what should I do?
Start with a conversation with your doctor rather than a crash diet. Ask to have your waist measured — more than 40 inches for men or 35 inches for women signals elevated metabolic risk even at moderate BMIs — along with blood pressure, blood sugar, and cholesterol. If weight loss is warranted, dropping just 5–10% of body weight measurably improves most of those markers.
Can I use this calculator for children or teens?
No — this tool is built for adults 20 and older. For ages 2 through 19, BMI is interpreted using CDC growth-chart percentiles that compare a child with peers of the same age and sex; the 5th to 85th percentile is considered healthy. A pediatrician can plot your child's number on the correct chart.