BMI Calculator
Calculate your body mass index (BMI) in metric or US units, see which weight category you fall into, and find the healthy weight range for your height.
What is BMI?
Body mass index is a simple screening number that relates your weight to your height. The formula is:
BMI = weight (kg) ÷ height (m)² · In US units: BMI = 703 × weight (lb) ÷ height (in)²
It was devised in the 1830s by the Belgian statistician Adolphe Quetelet and is still used worldwide because it needs nothing more than a scale and a tape measure.
BMI categories for adults
| BMI | Category (WHO, adults) |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Healthy weight |
| 25.0 – 29.9 | Overweight |
| 30.0 and above | Obesity |
Example: at 172 cm and 70 kg, BMI = 70 ÷ 1.72² = 23.7 — inside the healthy range, which for that height runs from about 54.7 kg to 73.7 kg.
What BMI can and can't tell you
BMI is a population screening tool, not a diagnosis. It says nothing about how your weight is distributed or how much of it is muscle:
- Athletes with high muscle mass often score "overweight" while carrying little fat.
- Older adults may have a "healthy" BMI while carrying too little muscle.
- Ethnic differences: health risks appear at lower BMIs in some Asian populations, so several countries use a lower overweight cutoff (23) locally.
Waist circumference, waist-to-height ratio, and body-fat percentage are common companions to BMI. A frequently cited rule of thumb: keep your waist under half your height.
A note on children
This calculator is for adults 20 and over. For children and teens, BMI is compared against age- and sex-specific growth charts (percentiles), because healthy body composition changes rapidly during growth.
Frequently asked questions
Is BMI accurate?
As a quick screen, yes — large studies show higher BMI correlates with higher risk of type 2 diabetes, heart disease, and joint problems. For any individual, it should be interpreted together with waist size, fitness, and medical history.
What is a good BMI for my height?
The healthy range (18.5–24.9) translates to a weight window for every height — the calculator shows yours after you enter your numbers.
Does BMI differ for men and women?
The adult formula and categories are the same for both sexes, even though women naturally carry more body fat. That's one of its known simplifications.
Should I make health decisions based on BMI alone?
No. Treat it as a starting point and discuss results with a healthcare professional — especially before starting a diet or exercise program.
This tool is for general information only and is not medical advice.