Calculate BMI with the standard weight and height formula, then check your category range.
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BMI (Body Mass Index) is a screening metric that estimates whether body weight is appropriate for height, calculated as weight(kg) ÷ height²(m²), and categorized on a standard scale.
Enter height and weight to see your BMI.
BMI (Body Mass Index) is a screening metric that estimates whether body weight is appropriate for height, calculated as weight(kg) ÷ height²(m²), and categorized on a standard scale.
Body Mass Index was developed by Belgian statistician Adolphe Quetelet in the 19th century and adopted by the WHO as a population-level screening tool. For adults, BMI under 18.5 is Underweight, 18.5–24.9 is Normal weight, 25–29.9 is Overweight, and 30+ is Obese.
BMI is widely used because it requires only height and weight — but it has known limitations. It doesn't distinguish between fat and muscle mass, so muscular athletes often show as 'overweight'. It's also less accurate for elderly populations (who lose muscle mass) and doesn't account for fat distribution (central/abdominal fat carries more health risk than hip/thigh fat). Use BMI as one data point among several, not as a standalone health diagnosis.
Choose metric (kg / cm) or imperial (lbs / inches) depending on your preferred measurements. Metric gives the most consistent result — avoid mixing unit systems.
Type your height and weight into the fields. The calculator accepts decimal values. For imperial, enter height in feet and inches (e.g., 5 ft 9 in = 5 and 9), not total inches.
Your BMI is calculated instantly and placed in a WHO category: Underweight (<18.5), Normal weight (18.5–24.9), Overweight (25–29.9), or Obese (≥30). The healthy weight range for your height is also shown.
The calculator shows the weight range for a BMI of 18.5–24.9 at your height. Use this as a reference range, not a personal target — body composition and fitness matter more than a single number.
WHO guidance suggests measuring waist circumference alongside BMI. Health risk increases above 94 cm (37 in) for men and 80 cm (31.5 in) for women, regardless of BMI category.
Common real-world scenarios where this tool saves time.
Track BMI changes over time to understand broad trends in your weight relative to height.
Use BMI as one of several metrics when setting weight goals alongside body fat percentage and waist circumference.
Healthcare professionals use BMI to screen for weight categories that may correlate with health risks.
Some health insurance applications ask for BMI — calculate it here before filling out forms.
Input
Height: 175 cm · Weight: 70 kgOutput
BMI: 22.9 — Normal weight (18.5–24.9)BMI = 70 ÷ (1.75)² = 70 ÷ 3.0625 = 22.86. Healthy range for 175 cm: approximately 57–76 kg. This person is in the middle of the normal range.
Input
Height: 180 cm · Weight: 95 kg (rugby player, ~12% body fat)Output
BMI: 29.3 — classified as OverweightA rugby player with 95 kg and 12% body fat is healthier than the BMI suggests. BMI can't distinguish between muscle and fat — 95 kg of mostly muscle looks the same as 95 kg of mostly fat. Use body fat % for more meaningful assessment in athletic individuals.
BMI is computed from height and weight using the Quetelet index formula developed in the 1830s and adopted by the WHO as a population-level screening tool. The calculator maps the result to standard adult categories and derives the healthy weight range by back-calculating the 18.5–24.9 BMI range at the entered height.
Formula
Metric: BMI = weight(kg) ÷ height(m)²
Imperial: BMI = 703 × weight(lb) ÷ height(in)²
Healthy weight range: lower = 18.5 × height(m)²; upper = 24.9 × height(m)²Standard BMI ranges for adults. Some guidelines use different thresholds for specific populations (e.g., lower cutoffs in some Asian clinical guidelines).
| BMI Range | Category | Health Risk (general) |
|---|---|---|
| Below 18.5 | Underweight | Increased risk (nutrient deficiency, bone loss) |
| 18.5 – 24.9 | Normal weight | Lowest risk range |
| 25.0 – 29.9 | Overweight | Moderate risk (elevated blood pressure, cholesterol) |
| 30.0 – 34.9 | Obese Class I | High risk |
| 35.0 – 39.9 | Obese Class II | Very high risk |
| 40 and above | Obese Class III (morbid obesity) | Extremely high risk |
BMI is a screening tool, not a diagnostic measure. Interpret alongside waist circumference, body fat %, blood pressure, and clinician guidance.
BMI is one of several indicators used to assess weight-related health risk. Each has trade-offs.
| Metric | What it measures | Advantage over BMI | Key limitation |
|---|---|---|---|
| BMI | Weight relative to height squared | Simple; requires no equipment; widely used in clinical literature | Cannot distinguish muscle from fat |
| Waist circumference | Abdominal fat (visceral fat) | Directly measures dangerous central fat deposit | Does not account for height |
| Waist-to-height ratio | Waist size relative to height | Strong predictor of metabolic and cardiovascular risk | Less established in clinical guidelines |
| Body fat % | Proportion of total mass that is fat | Accurately distinguishes muscle from fat | Requires calipers or DEXA scan for accuracy |
| Waist-to-hip ratio | Fat distribution pattern (apple vs pear) | Assesses cardiovascular risk from fat distribution shape | Less predictive than waist circumference alone |
WHO recommends using BMI alongside waist circumference for a more complete cardiovascular risk assessment in clinical settings.
| Related tool | Use this tool when | Use related tool when |
|---|---|---|
| Body Fat Calculator | You need a quick weight-status screen with only height and weight. BMI is the standard metric on medical forms and in clinical population studies. | You want to distinguish muscle from fat. A 100 kg bodybuilder and a sedentary person at 100 kg have identical BMIs but very different body composition and health profiles. |
| Ideal Weight Calculator | You want to know your current weight-to-height category. | You want a target weight range. The ideal weight calculator applies multiple clinical formulas (Devine, Robinson, Hamwi) to estimate a target from height alone. |
| Calorie Calculator | You need a single number to represent current weight status. | You are planning a diet or fitness program and need daily calorie targets based on BMR, TDEE, and activity level. |
BMI identifies statistical risk at a population level — a BMI of 27 does not mean you have or will develop any condition. Interpret it alongside waist circumference, blood pressure, cholesterol, and a clinician's assessment before drawing conclusions.
For people under 20, standard WHO BMI cutoffs do not apply. Children use BMI-for-age percentile charts from the CDC or WHO. A BMI that is 'normal' for an adult may be in the overweight percentile for a 10-year-old, and vice versa.
BMI divides weight by height² and cannot distinguish muscle from fat. Professional athletes, bodybuilders, and people with high muscle mass regularly show as 'overweight' or 'obese' while having low body fat. Use the body fat calculator for a composition-aware assessment.
Imperial BMI requires the 703 multiplier: BMI = 703 × weight(lbs) ÷ height(in)². Without it, the result is roughly 6× smaller than the actual BMI. Always verify your calculator uses the correct formula for the selected unit system.
Asian and Asian-Pacific populations show increased cardiometabolic risk at lower BMI values. WHO Asia-Pacific guidelines suggest screening at BMI ≥23 (overweight) and ≥27.5 (obese equivalent) rather than 25 and 30. Discuss with your healthcare provider if these thresholds are relevant to you.
Likely cause: BMI does not account for body composition. Athletes and muscular individuals are frequently classified as overweight by BMI while having healthy or low body fat percentages.
Fix: Use the body fat calculator for a composition-aware assessment. Pair with waist circumference: a BMI of 27 with a healthy waist circumference (below 94 cm for men, 80 cm for women) carries a very different risk profile than the same BMI with high abdominal fat.
Likely cause: The imperial formula uses the approximation factor 703 (exact value ≈ 703.07), so rounding during unit conversion can produce differences of ±0.1–0.2.
Fix: Use metric (kg and cm) for the most consistent result. If you must use imperial, enter height in total inches (5 ft 10 in = 70 in), not feet, and verify the calculator applies the 703 multiplier.
Likely cause: Height is likely entered in the wrong unit — for example, entering 175 into a field expecting feet/inches when metric is selected, or entering cm when the field expects inches.
Fix: Check the unit toggle before entering values. In metric: height in centimeters (e.g., 175 for 175 cm). In imperial: height in feet and inches separately (e.g., 5 and 9 for 5 ft 9 in). Do not enter meters in a centimeter field.
BMI cannot distinguish muscle from fat. A 90 kg athlete with 10% body fat will score as 'overweight' using BMI. Use the Body Fat Calculator (which applies the US Navy measurement method) or DEXA scan for composition-aware assessment.
Adult BMI categories (18.5–24.9 normal) do not apply to children or teenagers. Paediatric weight assessment uses BMI-for-age percentile charts from the CDC or WHO, which compare to a reference population of the same age and sex.
BMI is a screening tool that flags population-level statistical risk, not an individual diagnosis. A single BMI number cannot diagnose obesity, metabolic syndrome, or any specific condition. Clinical assessment requires waist circumference, lab results, blood pressure, and a clinician's evaluation.
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For adults, the WHO classifies BMI as: Under 18.5 = Underweight, 18.5–24.9 = Normal weight, 25–29.9 = Overweight, 30+ = Obese. These thresholds are for adults only — children use age- and sex-specific percentile charts from the CDC or WHO.
BMI is a population screening tool, not a diagnostic measure. It correlates with body fat at a population level but cannot distinguish muscle from fat for individuals. Athletes often show as overweight or obese on BMI despite low body fat. Always interpret BMI alongside waist circumference, body fat percentage, blood pressure, and a clinician's assessment.
A BMI of 30 or higher is classified as obese. The WHO further divides obesity into Class I (30–34.9), Class II (35–39.9), and Class III / morbid obesity (40 and above). Each class carries progressively higher cardiovascular, metabolic, and surgical risk.
Yes. BMI cannot distinguish between muscle and fat — both add weight. A professional rugby player at 180 cm and 100 kg has a BMI of 30.9 (obese range) but may have 12% body fat and excellent cardiovascular health. For muscular individuals, the body fat percentage calculator is more informative than BMI.
The BMI formula itself doesn't change with age, but its accuracy as a health indicator does. Older adults (65+) often lose muscle mass while gaining fat, so a 'normal' BMI can mask unhealthy body composition. Some clinical guidelines recommend a slightly higher BMI target for adults over 65 to account for this.
Morbid obesity, also called Class III obesity or severe obesity, refers to a BMI of 40 or higher. At this level, the risk of obesity-related conditions — including type 2 diabetes, heart disease, sleep apnea, and certain cancers — is significantly elevated. Weight-loss surgery (bariatric surgery) is often considered at BMI ≥40 or ≥35 with serious comorbidities.
No — the standard BMI formula (weight/height²) is the same for both. However, men and women naturally have different body fat distributions at the same BMI. Women typically have higher body fat than men at the same BMI due to physiological differences. Some research suggests sex-specific BMI thresholds may be more meaningful, but the WHO and CDC still use the same universal categories.
Standard WHO BMI categories were validated primarily on middle-aged adults. For adults over 65, a BMI in the 22–27 range is often considered optimal — the slight upward adjustment accounts for age-related muscle loss and the protective effect of modest weight reserves during illness. Discuss interpretation with your healthcare provider.
This is a general estimate and not a medical diagnosis. Health information is for educational purposes only and is not medical advice. Consult a qualified healthcare provider before making health decisions.
Part of Calculator Tools
More free tools for the same workflow.
Estimate ideal weight using Devine, Robinson, Miller, and Hamwi formulas and compare the output range in one place.
Estimate body fat % with US Navy waist/neck/hip measurements or BMI method. Runs locally in your browser—never uploaded. Free for men and women.
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Reviewed by EverydayTools Editorial Team on 2026-05-03.