BMI Calculator for Adult Height and Weight
Calculate body mass index from metric or imperial height and weight. Read the result as an adult screening estimate, not an individual diagnosis.
BMI Calculator workspace
BMI is a population-level screening tool, not a medical diagnosis. It does not distinguish muscle from fat and can be misleading for athletes, pregnant individuals, the elderly, very short or very tall people, and some non-European populations. Consult a qualified clinician for personalised health advice.
Metric & Imperial Toggle
Switch between kilograms / centimetres and pounds / feet+inches with one click. We convert internally so the formula is always the canonical metric form.
Full WHO Category Bands
Underweight, Healthy, Overweight, Obese I/II/III — with WHO thresholds and a clear health-risk note for each category, not just the high-level label.
Healthy Weight Range
For your entered height, we compute the weight range that would land you in the WHO healthy band (BMI 18.5–24.9). Shown in your selected unit system.
100% Client-Side
Height, weight, and BMI calculations stay entirely on your device. No upload, no logging, no analytics tied to the numbers you enter.
BMI Calculator: Body Mass Index from Weight and Height
Calculate body mass index from metric or imperial height and weight. Read the result as an adult screening estimate, not an individual diagnosis. BMI is weight relative to height; it does not directly measure body fat or distinguish muscle from fat. Adult category labels are not appropriate for interpreting children's BMI. Clinical interpretation requires age, health history, and other measurements; use the cited guidance to understand these limitations.
How to use the BMI calculator
- Choose your unit system: Metric (kg, cm) or Imperial (lb, ft+in). Switching units clears the fields.
- Enter your weight — kilograms in metric mode, pounds in imperial mode.
- Enter your height — centimetres in metric, or feet and inches in imperial.
- Read your BMI and category card. It updates instantly as you type; no submit button.
- Check the healthy weight range shown for your height, then read the limitations below before acting on the number.
The exact BMI formula, with every variable defined
BMI was devised by Belgian statistician Adolphe Quetelet in the 1830s as a population-level measure. The modern definition adopted by the CDC and WHO is a single ratio. This tool computes it in metric form and converts imperial input internally, so both unit modes return the same number.
Metric formula (the canonical form this tool uses)
BMI = weight (kg) ÷ height (m)²Imperial shortcut (same one-decimal result)
BMI = 703 × weight (lb) ÷ height (in)²- weight (kg) — body mass in kilograms.
- height (m) — standing height in metres (centimetres ÷ 100).
- weight (lb) — body mass in pounds.
- height (in) — standing height in inches (feet × 12 + inches).
- 703 — the unit-conversion constant that maps lb/in² onto kg/m².
Internally this calculator never uses the 703 shortcut: in imperial mode it multiplies pounds by 0.45359237 to get kilograms and inches by 2.54 to get centimetres, then applies the metric formula. The result is rounded to one decimal place for display. The category cut-points come straight from the CDC Adult BMI Categories and the WHO obesity fact sheet.
Worked examples: input → step-by-step → result
Metric · 70 kg, 175 cm
height = 175 cm = 1.75 m
BMI = 70 ÷ (1.75)² = 70 ÷ 3.0625 = 22.857…
BMI = 22.9 → Healthy (18.5–24.9)
Healthy weight range for 175 cm: 18.5 × 1.75² = 56.7 kg to 25 × 1.75² = 76.6 kg.
Imperial · 154 lb, 5 ft 9 in
height = 5×12 + 9 = 69 in = 175.26 cm = 1.7526 m
weight = 154 × 0.45359237 = 69.85 kg
BMI = 69.85 ÷ (1.7526)² = 22.74… (703 shortcut: 703 × 154 ÷ 69² = 22.74)
BMI = 22.7 → Healthy (18.5–24.9)
Edge case · muscular build
A 100 kg, 180 cm athlete computes BMI = 100 ÷ 1.8² = 30.9 → Obese Class I, even at 12% body fat. The formula has no input for muscle mass, so it misclassifies dense, lean physiques. Read the result alongside body fat percentage, not on its own.
CDC & WHO BMI Categories & Risk Bands
| BMI Range | Category | Population Risk Level |
|---|---|---|
| Below 18.5 | Underweight | Low (but malnutrition/illness risk) |
| 18.5 – 24.9 | Healthy | Lowest — baseline reference |
| 25.0 – 29.9 | Overweight | Increased |
| 30.0 – 34.9 | Obese I | High |
| 35.0 – 39.9 | Obese II | Very high |
| 40.0 and above | Obese III | Extremely high |
Risk is a population-level statistical association, not a personal prediction.
Six Situations Where BMI Misclassifies You
1. Athletes & Muscular Builds
Muscle is denser than fat. An NFL linebacker can register as obese while having sub-10% body fat. BMI cannot see body composition.
2. The Elderly
Sarcopenia (age-related muscle loss) lowers BMI even as visceral fat rises. A “healthy” BMI in an 80-year-old may mask metabolic risk.
3. South Asian & East Asian Populations
Some bodies show metabolic disease risk earlier than the European-derived thresholds suggest. The WHO supports 23 as the overweight cut-point for South Asians.
4. Pregnant or Post-Partum
BMI categories don't apply during pregnancy or in the first months post-partum. Use specialised obstetric guidelines instead.
5. Children & Adolescents
Paediatric BMI uses age-and-sex percentile charts (CDC / WHO growth standards), not the adult cut-points. Different tool.
6. Very Short or Very Tall
BMI scales with height squared, but humans don't. Tall people are systematically over-classified, short people under-classified.
Metrics That Improve on BMI for Individual Assessment
| Metric | What It Measures | How To Get It |
|---|---|---|
| Waist circumference | Abdominal fat (the dangerous kind) | Tape measure at navel level |
| Waist-to-height ratio | Abdominal fat relative to body size | Waist / height; target ≤ 0.5 |
| Body fat percentage | Actual lean vs adipose mass | DEXA scan, bioimpedance scale, calipers |
| Resting heart rate | Cardiovascular fitness | Fitness tracker, manual pulse-count |
| HbA1c / lipid panel | Metabolic disease markers | Annual physician blood test |
A modern, evidence-based annual check-up uses BMI as one of five or six inputs — not as the headline. If your BMI surprises you, ask your clinician to interpret it alongside at least waist circumference and a basic blood panel.
The nuance most BMI calculators skip: ethnicity-adjusted cut-points
The standard 25/30 thresholds were derived largely from white European adults and under-flag risk in some Asian populations. A WHO expert consultation (Lancet, 2004) found that type-2-diabetes and cardiovascular risk in many Asian groups rises at BMIs below 25, and recommended public-health trigger points at 23 (overweight) and 27.5 (obese). So a BMI of 24 reads “healthy” on the international scale but may already signal elevated risk for a South Asian adult.
BMI also has a built-in height bias: because it divides by height squared while body mass scales closer to height cubed, the formula systematically over-classifies tall people and under-classifies short people. Treat any single BMI number as a screening flag, not a measurement of body fat.
Medical disclaimer
For general informational purposes only — not medical advice. BMI is a screening estimate, not a diagnosis, and it cannot account for muscle mass, fat distribution, age, or ethnicity. Consult a qualified healthcare provider before making decisions about your health.
Category cut-points are cited above from the CDC and WHO. Last updated: September 15, 2026 · Runs 100% in your browser — no uploads, tool input is not sent to Toolk.
Related health & finance calculators
Measure what BMI cannot see — the US Navy tape method
Calorie CalculatorFind your BMR and TDEE for daily intake targets
Water Intake CalculatorDaily hydration target from your weight
Age CalculatorExact age — BMI guidance is age-conditional
Percentage CalculatorWork out percent change in weight or progress
Tip CalculatorSplit a restaurant bill and add a gratuity
Mortgage CalculatorEstimate your monthly home-loan payment
Loan CalculatorMonthly payment and total interest on any loan
Compound Interest CalculatorProject savings growth over time
All Free CalculatorsBrowse the full health & finance toolset
Frequently asked questions
How does the calculator compute BMI for imperial units?
It never uses the 703 shortcut. Pounds are multiplied by 0.45359237 to get kilograms and inches by 2.54 to get centimetres, then the canonical metric formula (kg ÷ m²) is applied — so metric and imperial modes return the same number, rounded to one decimal place.
Why did I get an obese result even though I am muscular?
BMI divides weight by height squared and has no input for body composition. A 100 kg athlete at 180 cm scores 30.9 regardless of body-fat percentage, so dense, lean physiques get misclassified. Read the number alongside a direct body-fat measure instead.
Are the same cut-points correct for every ethnicity?
No. A WHO expert consultation published in The Lancet found cardiometabolic risk rises below BMI 25 in many Asian populations and suggested trigger points of 23 (overweight) and 27.5 (obese) there. This tool labels with the standard CDC/WHO bands, so interpret Asian results with the lower thresholds in mind.
Does entering my height and weight upload anything?
No. The calculation is processed locally in your browser, and Toolk's page analytics do not receive your height or weight. Tool input is not sent to Toolk, and the page keeps working offline once loaded.
What should I measure next if my BMI looks off?
Use the Body Fat Calculator at /tools/body-fat-calculator — the US Navy tape method estimates what BMI cannot see (lean versus fat mass), and waist-to-height ratio at or below 0.5 adds the abdominal-risk context.