Body Mass Index is the quickest way to screen whether your weight is in a healthy range for your height. It is a single number — your weight in kilograms divided by your height in meters squared — that doctors, insurers and fitness coaches have used for decades as a first check. This calculator works in metric (cm, kg) and imperial (feet/inches, pounds), so you never have to convert units by hand.
Type your numbers in, and you get your BMI, the category it falls into, and the weight range that would put you in the healthy band for your height. Keep in mind it is a screening tool, not a diagnosis: athletes with a lot of muscle and older adults with less muscle can get misleading readings, which is why the limits section below matters.
Part of the Health Calculators collection on CountCrunch.
How BMI is calculated
The formula is simple enough to do on a calculator, but the unit conversions are where people slip up.
Example: someone 1.75 m tall weighing 70 kg has a BMI of 70 ÷ (1.75 × 1.75) = 22.9, squarely in the healthy range. In imperial units, 5′9″ and 154 lb gives 703 × 154 ÷ 69² ≈ 22.7 — same answer, different route.
BMI categories for adults
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Healthy weight |
| 25.0 – 29.9 | Overweight |
| 30.0 and above | Obesity |
These cutoffs come from the World Health Organization and apply to adults aged 20 and over. Children and teens use BMI-for-age percentiles instead, because healthy BMI changes as they grow.
What BMI does not tell you
- Muscle vs fat. A muscular athlete can land in "overweight" while being very lean. Pair BMI with the body fat calculator for a fuller picture.
- Fat location. Belly fat carries more health risk than fat elsewhere; BMI cannot see the difference.
- Age and sex. At the same BMI, women typically carry more body fat than men, and older adults more than younger ones.
If your BMI is outside the healthy range, treat it as a prompt to talk to a clinician or dietitian — not as a verdict on its own.
Frequently asked questions
What is a good BMI?
For most adults, a BMI between 18.5 and 24.9 is considered healthy. It is a screening range rather than a personal target — where you feel best within or near it depends on muscle, age and health history.
How do I calculate BMI with feet and inches?
Multiply your weight in pounds by 703, then divide by your height in inches squared. At 5′9″ (69 in) and 154 lb: 703 × 154 ÷ 69² ≈ 22.7. The calculator above does the conversion for you.
Is BMI accurate for athletes?
Often not. Muscle is denser than fat, so very muscular people can have an "overweight" BMI while being lean. Athletes get more from body fat percentage or waist measurements.
Does BMI work for children?
Not with adult cutoffs. Children and teens are assessed with BMI-for-age percentiles that account for growth. Ask a pediatrician for the right chart.
What BMI is considered obese?
A BMI of 30 or higher is classified as obesity in adults (30–34.9 class I, 35–39.9 class II, 40+ class III).