BMI Calculator
Calculate your Body Mass Index in metric (cm / kg) or imperial (ft / in / lbs). See your CDC / WHO category, healthy weight range, distance to range, and four clinical IBW formulas — all in your browser.
What you'll use this for
Health check-up
Quick reference before a doctor visit or annual physical.
Fitness goal setting
Compare current BMI to a healthy target range.
Diet planning
Pair BMI with calorie targets to set realistic milestones.
Forms
Many insurance and medical intake forms ask for BMI.
How to calculate BMI
Pick your unit system
Metric uses centimeters and kilograms. Imperial uses feet/inches and pounds.
Enter height & weight
Result updates instantly — no submit button.
Read your category
CDC / WHO categories: underweight, healthy weight, overweight, Class I / II / III obesity. Athletes and pregnant people need different metrics.
See healthy weight range
This is the weight range matching BMI 18.5–24.9 for your height — what the CDC, NIH, NHLBI, and AHA recommend as a weight goal.
(Optional) Compare clinical IBW formulas
Select your sex to see the four standard ideal-body-weight formulas (Devine, Robinson, Miller, Hamwi) — these are clinical heuristics primarily used for medication dosing.
Frequently asked questions
BMI is weight in kilograms divided by height in meters squared (kg/m²). It is a screening tool, not a diagnosis. Athletes with high muscle mass may register as overweight despite low body fat; pregnant people, older adults, and children require different assessments.
CDC / WHO adult categories: below 18.5 = underweight (with WHO sub-tiers: severe thinness <16, moderate 16–16.9, mild 17–18.4), 18.5–24.9 = healthy weight, 25.0–29.9 = overweight, 30.0–34.9 = Class I obesity, 35.0–39.9 = Class II obesity, 40.0+ = severe obesity (Class III). Children and teens use age-and-sex percentile charts instead.
The healthy weight range is the weight that puts your BMI between 18.5 and 24.9 for your height. This is what the CDC, NIH / NHLBI, and American Heart Association recommend as the target for weight goals — not the clinical IBW formulas below.
Devine (1974), Robinson (1983), Miller (1983), and Hamwi (1964) are clinical heuristics that were originally developed for medication dosing, not personal weight goals. They typically vary by 5–10 lbs because they were derived from different populations. Doctors use them in clinical settings; for a weight target, the BMI-based healthy range is what major health organizations recommend.
Your BMI divided by 25 (the upper bound of the healthy range). Below 1.0 means you are inside the healthy range; above 1.0 means you are outside it.
No. The formula runs entirely in your browser. Your height, weight, and age never leave your device.
About BMI
Body Mass Index (BMI) was published by Belgian astronomer-statistician Adolphe Quetelet in 1832 as a population-level statistic. It became the WHO’s default body-size indicator in 1995 because it is cheap, easy, and reasonably correlated with body-fat percentage at the population level.
Formula
BMI = kg / m² or BMI = (lbs / in²) × 703
Adult BMI categories (CDC / WHO)
- < 18.5 — Underweight (WHO sub-tiers: severe <16 · moderate 16–16.9 · mild 17–18.4)
- 18.5 – 24.9 — Healthy weight
- 25.0 – 29.9 — Overweight
- 30.0 – 34.9 — Class I obesity
- 35.0 – 39.9 — Class II obesity
- ≥ 40.0 — Severe obesity (Class III)
The four clinical ideal-body-weight (IBW) formulas
Each was derived from different actuarial / clinical data, so they disagree by 5–10 lbs at typical adult heights. None is officially endorsed as a weight goal by the CDC or NIH; they are clinical heuristics primarily used for medication dosing.
- Devine (1974) — Male: 50 kg + 2.3 kg per inch over 60". Female: 45.5 kg + 2.3 kg per inch over 60".
- Robinson (1983) — Male: 52 kg + 1.9 kg per inch. Female: 49 kg + 1.7 kg per inch.
- Miller (1983) — Male: 56.2 kg + 1.41 kg per inch. Female: 53.1 kg + 1.36 kg per inch.
- Hamwi (1964) — Male: 48 kg + 2.7 kg per inch. Female: 45.5 kg + 2.2 kg per inch.
What BMI does well
- Quick screening across large populations
- Fits naturally on health intake forms
- No special equipment beyond a scale and a tape measure
What BMI doesn’t do
- Distinguish muscle from fat (athletes can read as overweight)
- Account for body shape, fat distribution, or ethnicity
- Apply to children — they need age-and-sex percentile charts
- Replace a doctor’s judgement — pair it with waist circumference, blood pressure, lipids, and lifestyle factors
Sources: CDC Adult BMI Categories · NIH / NHLBI BMI calculator · American Heart Association — BMI in adults.