BMI Calculator
Calculate your Body Mass Index and see which healthy weight category you fall into — instant, free, no sign-up.
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BMI is a general screening tool and does not directly measure body fat or account for muscle mass, age, or sex. Consult a healthcare provider for personalized advice.
Calculating BMI for a child or teenager? See how age and sex change the calculation.
Where BMI Comes From, and What It Doesn't Measure
BMI was devised in the 1830s by the Belgian mathematician Adolphe Quetelet as a population-level statistic, not a personal diagnostic tool. Public health bodies adopted it decades later because it's cheap to calculate and correlates reasonably well with body fat across large groups — which is also exactly where its limits show up for any one individual.
Limitations of BMI
- Doesn't distinguish muscle from fat. Two people with identical BMI can have very different body compositions — a muscular athlete and someone with low muscle mass can land on the same number.
- Doesn't account for fat distribution. Where fat is stored, especially around the waist, matters for health risk, and BMI can't see that.
- Less reliable at the extremes of age. Growing children, teenagers, and older adults with reduced muscle mass need different reference standards, not the adult ranges shown here.
- Varies by ethnicity. Some population groups face higher health risks at lower BMI thresholds than the standard cutoffs reflect.
Use it as a quick screening starting point, not a verdict. Sources: WHO obesity and overweight fact sheet and the CDC adult BMI guidance.
What Is BMI?
Body Mass Index (BMI) is a simple screening measure that uses your height and weight to estimate whether you fall into an underweight, normal, overweight, or obese range. It's the same formula doctors' offices and public health bodies like the WHO and CDC use for a quick, population-level check — not a diagnosis.
How BMI Is Calculated
BMI = weight (kg) ÷ height (m)². In imperial units: BMI = 703 × weight (lb) ÷ height (in)².
- Underweight: below 18.5
- Normal weight: 18.5–24.9
- Overweight: 25–29.9
- Obese: 30 and above
Example
A person weighing 70 kg at 1.75 m tall: 70 ÷ (1.75 × 1.75) = 22.9 → Normal weight.
Tracking a weight goal? Use our Date Calculator to count down the days to your target date, or the Percentage Calculator to see what percentage of your starting weight you have lost so far.
Learn more: How to Calculate BMI: A Complete Guide, Ideal Weight vs BMI, and How Often Should You Check Your BMI?, and How BMI Calculations Differ for Athletes and Muscular Body Types
FAQ
Is BMI accurate for athletes or muscular people? Not always. BMI doesn't distinguish muscle from fat, so muscular individuals can show as "overweight" despite low body fat. It's a screening tool, not a diagnosis.
Does BMI apply the same way to children? No. Children and teens are measured against age- and sex-specific percentile charts, not the adult categories shown here.
Can BMI be too low even in the "normal" range? Yes — frame size, age, and muscle mass mean two people with the same BMI can have very different health profiles. Use BMI as a starting point, not a final answer.
How often should I check my BMI? There's no fixed rule — most people check it occasionally alongside other health markers rather than tracking it daily.
Common BMI Examples
Sample BMI results for common height and weight combinations — enter your own numbers in the calculator above for an exact result.
- 5'6" (167 cm), 65 kg (143 lbs)
BMI = 23.3 — Normal - 5'8" (173 cm), 80 kg (176 lbs)
BMI = 26.7 — Overweight - 5'4" (163 cm), 55 kg (121 lbs)
BMI = 20.7 — Normal - 6'0" (183 cm), 95 kg (209 lbs)
BMI = 28.4 — Overweight - 5'2" (157 cm), 45 kg (99 lbs)
BMI = 18.3 — Underweight - 5'10" (178 cm), 100 kg (220 lbs)
BMI = 31.6 — Obese
Methodology and assumptions
BMI is weight in kilograms divided by height in metres squared. Adult category labels follow the general WHO thresholds shown on the page. BMI is a screening ratio, not a direct measurement of body fat or an individual diagnosis.
Authoritative sources
- Obesity and overweight: BMI definition and limitationsWorld Health Organization
Sources last checked September 10, 2026. Regulations and guidance can change; use the linked authority for the current position.
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Content maintained by Ajit Naskar. Medical review status: Not independently reviewed by a qualified clinician. Existing content is frozen against substantive expansion; sources and limitations were last audited on September 10, 2026.