BMI Calculator
Height and weight in, BMI out — with your category and the healthy weight range for your height.
Body mass index (BMI) is the standard screening number doctors, insurers and fitness programs use to relate weight to height: weight in kilograms divided by height in meters squared. This calculator handles the unit conversions for you — enter feet/inches and pounds, or centimeters and kilograms — and returns your BMI, the category it falls in, and something more actionable: the weight range considered healthy for your height.
The categories follow the World Health Organization ranges used in US clinical practice: under 18.5 is underweight, 18.5–24.9 normal, 25–29.9 overweight, and 30+ obese. Worth saying plainly: BMI is a population screening tool, not a diagnosis. It can't tell muscle from fat — plenty of athletes are "overweight" by BMI while being extremely lean — and it applies differently to children, pregnant women and older adults. Treat the number as a conversation starter with a doctor, not a verdict. Everything computes in your browser; nothing about your body is sent anywhere. Tracking weight goals against a budget or timeline? The percentage calculator handles percent-change math cleanly.
How to use the BMI Calculator
- Pick your units — US (feet, inches, pounds) or metric (centimeters, kilograms).
- Enter your height and weight.
- Read your BMI, its category, and the healthy weight range for your height.
- Adjust the weight number to see what BMI a goal weight would give you.
What the number leaves out
BMI uses only your height and weight, which is what makes it quick — and also what makes it blunt. It cannot tell muscle from fat, so a muscular, lean person often reads as overweight while carrying very little fat. It says nothing about where fat sits, even though fat around the waist carries more health risk than fat elsewhere, and it applies the same thresholds regardless of age or sex.
None of that makes BMI useless — it's a genuinely handy screening number for spotting a trend over time or a value far outside the healthy range. It just isn't a verdict on any single body. Read it as one low-effort data point alongside things like waist size and activity, not a scorecard. Our guide on understanding BMI and its limits covers this in more depth.
Frequently asked questions
How is BMI calculated?
Weight in kilograms divided by height in meters squared (kg/m²). For US units the calculator converts first — the equivalent shortcut formula is 703 × pounds ÷ inches². A 5'10" person at 170 lbs is 170 × 703 ÷ 70² ≈ 24.4.
What are the BMI categories?
Under 18.5 is underweight, 18.5 to 24.9 is the normal range, 25 to 29.9 is overweight, and 30 and above is classed as obesity (with clinical subclasses at 35 and 40). These are the WHO cutoffs used across US healthcare.
Is BMI accurate for muscular people?
No — that's its best-known blind spot. Muscle is denser than fat, so muscular builds score "overweight" while carrying little fat. If that's you, waist circumference and body-fat percentage are far better measures; BMI simply wasn't built for you.
What's the healthy weight range shown?
The weights that would put your BMI between 18.5 and 24.9 at your height — the normal range. It's a wide band by design; where in it you personally do best depends on build, age and muscle, which is doctor territory.
Does BMI differ for children or by sex?
For adults the formula and cutoffs are the same for everyone. Children and teens use the same formula but age-and-sex percentile charts instead of fixed cutoffs — this calculator is for adults 20 and over.