BMI Calculator
Calculate your Body Mass Index free online. Enter your height and weight to get your BMI score, category, and healthy weight range instantly.
How to Use BMI Calculator
- 1Select your unit system: Metric (kg/cm) or Imperial (lbs/ft in).
- 2Enter your weight and height in the input fields.
- 3Click Calculate BMI to see your result.
- 4View your BMI score, category, healthy weight range, and visual scale bar.
- 5Use the Copy button to copy your BMI summary.
About BMI Calculator
Our BMI Calculator gives you your Body Mass Index in seconds using either metric or imperial units. See your BMI category (underweight, normal, overweight, obese) and your ideal healthy weight range. Includes a visual BMI scale bar showing exactly where you fall.
How BMI Calculator Works
Body Mass Index (BMI) is a numerical value derived from a person's weight and height. Developed by Belgian mathematician Adolphe Quetelet in the 1830s and later adopted by the World Health Organization, it remains the most widely used population-level screening tool for weight categories. The calculation divides your weight in kilograms by the square of your height in metres. Because height is squared, taller people need proportionally more weight to achieve the same BMI as shorter people. The WHO classifies BMI into six ranges from severe thinness (below 16) all the way to obese class III (40 and above). For imperial units the formula uses a conversion factor of 703 to account for the difference between pounds/inches and kilograms/metres. Our calculator handles both unit systems and also computes BMI Prime — your BMI expressed as a fraction of the healthy upper limit of 25 — giving you an at-a-glance sense of how far you are from the ideal range. Healthy weight ranges by height are also displayed so you can set a concrete goal.
BMI = weight (kg) ÷ height (m)²
Imperial: BMI = 703 × weight (lbs) ÷ height (inches)²
BMI Prime = BMI ÷ 25Example: calculating BMI for a 75 kg person who is 1.75 m tall
- Square the height: 1.75 × 1.75 = 3.0625 m²
- Divide weight by the squared height: 75 ÷ 3.0625 = 24.49
- BMI Prime: 24.49 ÷ 25 = 0.98 (just within the healthy range)
BMI = 24.5 → Normal weight (WHO classification)
Reference Data
WHO BMI Classification for Adults
| Category | BMI Range | BMI Prime | Health Risk |
|---|---|---|---|
| Severe Thinness | < 16.0 | < 0.64 | Very high |
| Moderate Thinness | 16.0 – 16.9 | 0.64 – 0.67 | High |
| Mild Thinness | 17.0 – 18.4 | 0.68 – 0.73 | Moderate |
| Normal Weight | 18.5 – 24.9 | 0.74 – 1.00 | Low |
| Overweight | 25.0 – 29.9 | 1.00 – 1.20 | Increased |
| Obese Class I | 30.0 – 34.9 | 1.20 – 1.40 | High |
| Obese Class II | 35.0 – 39.9 | 1.40 – 1.60 | Very high |
| Obese Class III | ≥ 40.0 | ≥ 1.60 | Extremely high |
Healthy Weight Range by Height (BMI 18.5–24.9)
| Height | Min Healthy Weight | Max Healthy Weight |
|---|---|---|
| 160 cm (5'3") | 47.4 kg (104 lbs) | 63.7 kg (140 lbs) |
| 165 cm (5'5") | 50.4 kg (111 lbs) | 67.8 kg (149 lbs) |
| 170 cm (5'7") | 53.5 kg (118 lbs) | 72.0 kg (158 lbs) |
| 175 cm (5'9") | 56.7 kg (125 lbs) | 76.3 kg (168 lbs) |
| 180 cm (5'11") | 59.9 kg (132 lbs) | 80.7 kg (178 lbs) |
| 185 cm (6'1") | 63.3 kg (140 lbs) | 85.2 kg (188 lbs) |
| 190 cm (6'3") | 66.8 kg (147 lbs) | 89.9 kg (198 lbs) |
| 195 cm (6'5") | 70.4 kg (155 lbs) | 94.7 kg (209 lbs) |
| 200 cm (6'7") | 74.0 kg (163 lbs) | 99.6 kg (219 lbs) |
Who Uses This Tool and Why
- ✓Healthcare professionals use BMI as a quick triage screen to identify patients who may need further metabolic testing or dietary counselling.
- ✓Individuals tracking a weight-loss or muscle-building journey use BMI alongside waist circumference and body-fat percentage to monitor progress.
- ✓Insurance companies and clinical trials use BMI as an eligibility or risk-stratification criterion — knowing yours helps you understand your classification.
- ✓Parents and paediatricians use age-adjusted BMI percentile charts to track healthy growth patterns in children and teenagers.
- ✓Epidemiologists and public-health researchers use population-level BMI data to study the prevalence of obesity and its correlation with chronic disease.
Limitations & Practical Tips
Known Limitations
- •BMI does not distinguish between fat mass and lean muscle mass — a heavily muscled athlete may register as "overweight" despite low body fat.
- •The WHO cutoffs were derived largely from European populations and may not accurately reflect health risk in Asian, African, or Pacific Islander groups.
- •BMI does not account for fat distribution — visceral (abdominal) fat is more metabolically dangerous than subcutaneous fat, but BMI cannot detect this.
- •In older adults, BMI can underestimate obesity because muscle mass decreases with age, making room for more fat at the same body weight.
- •For children and adolescents, absolute BMI values are not used; age- and sex-specific percentile charts are required for meaningful interpretation.
Tips for Best Results
- →Use BMI as a starting point, not a verdict. Pair it with waist-to-height ratio (a value below 0.5 is generally healthy) for a more complete picture.
- →If your BMI is borderline (e.g. 24.5 or 25.5), a DEXA scan or bioelectrical impedance analysis can tell you your actual body fat percentage.
- →Weight fluctuates by 1–2 kg throughout the day due to food, water, and clothing. Weigh yourself first thing in the morning for the most consistent readings.
- →For children, always use a growth chart (such as the CDC or WHO charts) and consult a paediatrician rather than comparing to adult BMI cutoffs.
Frequently Asked Questions
- What is a healthy BMI range?
According to the World Health Organization, a BMI between 18.5 and 24.9 is considered normal weight for adults. Below 18.5 is underweight, 25–29.9 is overweight, and 30 or above is classified as obese.
- Is BMI an accurate measure of health?
BMI is a useful screening tool but has limitations — it does not directly measure body fat percentage or muscle mass. Athletes may have a high BMI due to muscle, while older adults may have a normal BMI but high body fat. Use BMI alongside other health indicators.
- What is the formula for BMI?
In metric units: BMI = weight (kg) ÷ height (m)². In imperial units: BMI = 703 × weight (lbs) ÷ height (inches)². Our calculator handles both unit systems automatically.
- What is BMI Prime?
BMI Prime is your BMI divided by 25 (the upper limit of the healthy range). A value of 1.0 means you are exactly at the upper healthy limit. Values below 0.74 indicate underweight, 0.74–1.0 is healthy, and above 1.0 is overweight.
- How is BMI different for children vs. adults?
For adults (20+), fixed BMI cutoffs apply regardless of age or sex. For children and teenagers (2–19), age- and sex-specific percentile charts are used. A child with the same BMI number as an adult may be in a completely different weight category depending on their age and sex.
- What is the BMI cutoff for obesity surgery eligibility?
In most clinical guidelines, bariatric (weight-loss) surgery is considered for adults with BMI ≥ 40, or BMI ≥ 35 with obesity-related health conditions like type 2 diabetes or hypertension. These thresholds vary by country and clinical protocol.
- Can BMI predict disease risk?
At a population level, higher BMI correlates with increased risk of type 2 diabetes, cardiovascular disease, hypertension, certain cancers, and sleep apnoea. However, at the individual level, BMI is a weak predictor — many people with high BMI are metabolically healthy, and some with normal BMI have high cardiovascular risk due to visceral fat.
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Last updated: May 2, 2026 — BMI Calculator by CalcDash.