BMI Calculator
Your BMI in US or metric units — plus an honest explanation of what the number does and doesn't mean.
Calculate your body mass index
How BMI is calculated
Body mass index is your weight divided by the square of your height, in metric units:
Example: someone 5'10" (70 inches) weighing 175 pounds has a BMI of 703 × 175 ÷ 70² = 25.1. The standard adult categories used by the CDC and WHO are: under 18.5 underweight, 18.5–24.9 healthy weight, 25–29.9 overweight, and 30+ obesity.
What BMI is actually for
BMI was designed as a quick screening tool for populations, and at that job it's genuinely useful: it costs nothing, requires only a scale and a tape measure, and correlates with body fat across large groups. Public-health researchers and doctors use it as a first-pass flag — a reason to look closer, not a verdict.
What BMI can't tell you
BMI cannot distinguish muscle from fat, doesn't know where you carry weight, and ignores age, sex, and frame. A muscular athlete can score "overweight" while carrying very little body fat; an older adult can score "healthy" while carrying little muscle. Waist circumference, body-fat percentage, blood pressure, and lab work all say more about health than BMI alone. Treat the number as one data point — if it surprises you in either direction, that's a conversation to have with a doctor, not a diagnosis to give yourself.
If you want to change the number
Sustainable change is unglamorous: a modest calorie adjustment, more protein and whole foods, resistance training to keep or build muscle, regular sleep, and patience measured in months. Crash approaches move the scale fast and reverse just as fast. If weight is tangled up with stress or eating patterns that feel out of your control, a doctor or registered dietitian is the right next step — that's what they're for.
Frequently asked questions
Is BMI accurate for athletes?
Often not. Muscle is denser than fat, so muscular people frequently score 'overweight' or higher while being lean. For athletes, body-fat percentage and waist measurements are far more informative.
Does this calculator work for children?
No — these are adult categories. Children and teens use BMI-for-age percentiles that account for growth, which require different charts. A pediatrician can interpret those properly.
What's a healthy weight for my height?
The calculator shows the weight range corresponding to a BMI of 18.5–24.9 for your height. It's a general screening range, not a personal target — the right number for you depends on muscle, age, and overall health.
Should I worry about a BMI of 25–27?
Not panic — context matters. BMI slightly over 25 with good waist measurement, blood pressure, and labs is very different from the same number with poor markers. Discuss trends and the full picture with a doctor.
Is BMI different for men and women?
The standard formula and categories are identical for adult men and women, which is one of its known limitations — women naturally carry more body fat at the same BMI. It's another reason BMI is a screening tool, not a complete measure.