BMI Calculator
Body mass index with metric or imperial units, your category, and the healthy weight range for your height — private and instant.
Your files never leave your device.
How to use the BMI calculator
- Pick your units — metric (kilograms, centimeters) or imperial (pounds, feet and inches).
- Enter weight and height. Your BMI, category and the healthy weight range for your height appear instantly — no button to press.
Understanding your BMI
BMI — body mass index — is your weight divided by your height squared (kg/m²). For imperial units, the formula is 703 × pounds ÷ inches². The result falls into four WHO categories:
- Below 18.5 — underweight
- 18.5 to 24.9 — healthy range
- 25.0 to 29.9 — overweight
- 30.0 and above — obese
The healthy range shown works backwards from your height: the weight span corresponding to a BMI of 18.5 to 24.9. It's a more actionable number than BMI itself — it answers "what should I weigh?" directly.
What BMI can't tell you
BMI is a population-screening tool, not a personal diagnosis. It can't distinguish muscle from fat — a trained athlete can read as "overweight" while carrying very little fat, and someone with a normal BMI can carry more fat than is healthy (sometimes called "normal weight obesity"). It also ignores age, sex, bone density and where fat sits on the body; belly fat around the organs is far riskier than fat on the hips at the same BMI. For a fuller picture, waist circumference (men under 94 cm / 37 in, women under 80 cm / 31.5 in) and body-fat percentage add what BMI misses. And for children and teens, age- and sex-specific percentile charts are required — this calculator is built for adults.
When BMI is useful
As a starting point and a trend line. A single BMI reading tells you little; watching it move over months while you change habits tells you a lot. It's also the number most health questionnaires and insurance forms ask for, so having it calculated correctly (unit conversions are where people usually slip) is worth the five seconds this page takes. Whatever you read, remember: one number never tells the whole story of a body.
Frequently asked questions
How is BMI calculated?
BMI = weight in kilograms divided by height in meters squared. For imperial units: BMI = 703 × pounds ÷ inches². Example: 70 kg at 1.75 m gives 70 ÷ (1.75 × 1.75) = 22.9.
What is a healthy BMI range?
For adults: below 18.5 is underweight, 18.5–24.9 is the healthy range, 25–29.9 is overweight, 30 and above is obese. These are WHO population-level categories, not individual diagnoses.
Is BMI accurate for athletes or muscular people?
No — BMI cannot tell muscle from fat. A muscular athlete can show as overweight while being lean. It also ignores age, sex and body fat distribution. Treat it as a rough screening number, not a verdict; waist circumference and body-fat percentage tell more.
Does this BMI calculator work for children?
No. Children and teens need age- and sex-specific BMI percentile charts — this calculator is for adults (20+). For children, consult pediatric growth charts or a doctor.
Is my data private?
Yes. All calculations run in your browser. Nothing is uploaded, logged or stored — you can even use it offline after the page loads.