Zuletzt aktualisiert: 21. August 2026
BMI-Rechner
Ersteller
Dharmendra SinghPrüfer
Ersteller
Dharmendra SinghPrüfer
Quick Answer
The BMI (Body Mass Index) Calculator computes BMI using the formula BMI = weight (kg) / height (m)² in metric units or BMI = 703 × weight (lb) / height (in)² in imperial units. It classifies the result into six WHO adult categories: Underweight (<18.5), Normal weight (18.5–24.9), Overweight (25–29.9), Obese Class I (30–34.9), Obese Class II (35–39.9), and Obese Class III (≥40). The calculator also returns the healthy weight range for the entered height and the amount of weight to gain or lose to reach that range.
To calculate BMI, divide your weight in kilograms by your height in metres squared. A healthy BMI for adults is between 18.5 and 24.9. Below 18.5 is Underweight; 25 to 29.9 is Overweight; 30 and above is Obese. In imperial units, multiply your weight in pounds by 703 and divide by your height in inches squared.
Wichtige Erkenntnisse
- BMI = kg ÷ m² (metric) or 703 × lb ÷ in² (imperial); the WHO healthy adult range is 18.5–24.9.
- WHO defines six adult categories: Underweight (<18.5), Normal (18.5–24.9), Overweight (25–29.9), Obese I/II/III (30/35/40+).
- BMI cannot distinguish muscle from fat — athletes may be misclassified; use body fat % for a fuller picture.
- Asian populations may develop metabolic disease at BMI ≥ 23 (overweight) and ≥ 27.5 (obese) — lower than global thresholds.
- The safest long-term weight-loss rate is 0.5–1 kg (1–2 lb) per week through a moderate calorie deficit.
Ersteller
Dharmendra SinghPrüfer
Ersteller
Dharmendra SinghPrüfer
Formel
Metric: BMI = kg / m² | Imperial: BMI = 703 × lb / in²
Wobei:
- BMI=Body Mass Index(kg/m²)
- weight=Body weight(kg or lb)
- height=Body height(m or in)
- 703=Imperial conversion factor (lb/in² → kg/m²)
Rechenbeispiele
Adult — Metric, Normal Weight
A 30-year-old adult who is 175 cm tall and weighs 70 kg wants to check their BMI and confirm they are in the healthy range.
- 1Convert height: 175 cm = 1.75 m
- 2Apply formula: BMI = 70 / (1.75)² = 70 / 3.0625
- 3BMI = 22.857 → rounded to 22.9 kg/m²
- 4Category: Normal weight (18.5 – 24.9)
- 5Healthy weight range: 18.5 × 3.0625 = 56.7 kg (min); 24.9 × 3.0625 = 76.3 kg (max)
- 6Current weight 70 kg is within the healthy range → weightToLose = 0, weightToGain = 0
Adult — Metric, Overweight
A 45-year-old who is 170 cm tall and weighs 85 kg wants to know how much weight to lose to reach a healthy BMI.
- 1Convert height: 170 cm = 1.70 m
- 2Apply formula: BMI = 85 / (1.70)² = 85 / 2.89
- 3BMI = 29.412 → rounded to 29.4 kg/m²
- 4Category: Overweight (25.0 – 29.9)
- 5Healthy max weight: 24.9 × 2.89 = 71.961 → 72.0 kg
- 6Weight to lose: 85 − 72.0 = 13.0 kg
Adult — Imperial, Normal Weight
An adult who is 5 feet 10 inches tall and weighs 154 pounds checks their BMI using imperial units.
- 1Convert height: 5 ft 10 in = (5 × 12) + 10 = 70 inches
- 2Apply imperial formula: BMI = 703 × 154 / 70²
- 3BMI = 108262 / 4900 = 22.094 → rounded to 22.1
- 4Category: Normal weight (18.5 – 24.9)
- 5Healthy weight range: 18.5 × 4900 / 703 = 128.9 lb (min); 24.9 × 4900 / 703 = 173.6 lb (max)
- 6Current weight 154 lb is within the healthy range → weightToLose = 0, weightToGain = 0
Einführung
The BMI Calculator computes your Body Mass Index — a widely used screening number derived from height and weight — and maps it to the six WHO adult weight categories: Underweight, Normal weight, Overweight, and three classes of obesity. This tool supports both metric (kg, cm) and imperial (lb, ft/in) unit systems and returns your BMI value, weight category, healthy weight range, and how much to gain or lose to reach that range. BMI is a starting point, not a diagnosis — always consult a healthcare professional for personalised advice.
How to Use the BMI Calculator
Select your preferred unit system (metric or imperial). For metric, enter your height in centimetres and weight in kilograms. For imperial, enter height as feet plus remaining inches, and weight in pounds. The calculator instantly returns your BMI (to one decimal place), your WHO weight category, and the healthy weight range for your height. The fields 'Weight to Lose' and 'Weight to Gain' show how many kilograms or pounds away from the healthy window you are — both will be zero if you are already within the normal range.
Select metric or imperial unit system
Enter height (cm, or feet + inches)
Enter weight (kg or lb)
Read BMI, category, healthy range, and gain/lose targets instantly
BMI Formula Explained
For metric units the formula is BMI = weight (kg) / height (m)². For imperial units the CDC/NHLBI formula is BMI = 703 × weight (lb) / height (in)². The factor 703 converts the ratio from lb/in² to the standard kg/m² unit. Both formulas produce the same dimensionless number when consistent unit conversions are applied. The metric form is exact; the imperial form introduces negligible rounding. For example, a person who is 175 cm (1.75 m) tall and weighs 70 kg has BMI = 70 / (1.75)² = 22.9. In imperial, a person who is 5 ft 10 in (70 in) and weighs 154 lb has BMI = 703 × 154 / 70² = 22.1.
Always convert height to metres before applying the metric formula. A common error is leaving height in centimetres, which produces results 10,000 times too large.
WHO BMI Categories for Adults
The World Health Organization defines six adult BMI categories. These thresholds apply regardless of age (for adults over 18) or sex, though both moderate their metabolic meaning. For clinical and research contexts a seventh sub-category — 'Severe Thinness' (BMI < 16.0) — is sometimes used within the Underweight bracket.
| BMI Range | WHO Category | Health Risk |
|---|---|---|
| < 16.0 | Severe Thinness | Very High |
| 16.0 – 18.4 | Underweight | High |
| 18.5 – 24.9 | Normal weight | Low (average) |
| 25.0 – 29.9 | Overweight | Increased |
| 30.0 – 34.9 | Obese Class I | High |
| 35.0 – 39.9 | Obese Class II | Very High |
| ≥ 40.0 | Obese Class III | Extremely High |
Healthy Weight Range and Target Weights
The healthy weight range is the set of body weights that correspond to a BMI between 18.5 and 24.9 for a given height. It is computed as: min weight = 18.5 × h² and max weight = 24.9 × h² (metric, h in metres), or min = 18.5 × in² / 703 and max = 24.9 × in² / 703 (imperial, height in inches). For a person 175 cm tall, the healthy range is 56.7–76.3 kg. For 5 ft 10 in that is 128.9–173.6 lb. If your current weight exceeds the upper bound, the difference is the recommended weight loss target. If it falls below the lower bound, the difference is a weight gain target. These figures are mathematical ideals — a physician or dietitian should set actual clinical targets.
Aim to lose no more than 0.5–1 kg (1–2 lb) per week through a modest calorie deficit of 500–1000 kcal/day. Rapid loss of more than 1–1.5 kg/week is associated with muscle wasting and nutrient deficiencies.
Limitations of BMI
BMI is a convenient population-level screening index, not a direct measure of body fat or metabolic health. Its primary limitations include: (1) Muscle mass: Athletes and strength trainers may have high BMI due to muscle, not fat. (2) Age: Older adults lose muscle and gain fat at the same weight, so the same BMI conceals increasing adiposity. (3) Sex: Women typically carry more fat than men at the same BMI. (4) Ethnicity: South Asian, East Asian, and some other populations develop metabolic complications at lower BMI values than the WHO thresholds were calibrated for. (5) Fat distribution: Central (abdominal) obesity is more harmful than peripheral fat; a BMI of 26 with a large waist circumference carries more risk than one with the same BMI and slim waist. For a more complete assessment, pair BMI with waist circumference, waist-to-hip ratio, body fat percentage, blood pressure, and blood glucose.
BMI cannot distinguish muscle from fat
BMI does not capture fat distribution (central vs. peripheral)
Elderly, pregnant, or muscular individuals should interpret results cautiously
Use supplemental measures: waist circumference, body fat %, and blood tests
Asian BMI Thresholds (WHO Asia-Pacific Guidelines)
The WHO Western Pacific Regional Office published Asia-Pacific thresholds in 2000 reflecting that people of Asian descent develop insulin resistance, hypertension, and type 2 diabetes at lower BMI values. The proposed Asian cut-offs are: Normal weight: 18.5 – 22.9; At risk: 23.0 – 24.9; Obese I: 25.0 – 29.9; Obese II: ≥ 30.0. Some national guidelines (Singapore Ministry of Health, Japan Society for the Study of Obesity) further recommend obesity intervention at BMI ≥ 27.5. If you are of South Asian, East Asian, or Southeast Asian descent, these lower thresholds may be more clinically relevant to you. Consult your physician for personalised guidance.
This calculator uses standard WHO global thresholds by default. The Asian thresholds are provided here for informational purposes.
BMI, Chronic Disease, and Mortality Risk
Large epidemiological studies consistently show a J-shaped or U-shaped relationship between BMI and all-cause mortality. Both very low and very high BMI values are associated with increased mortality. The lowest mortality is typically observed in the BMI 22–25 range. Overweight (25–29.9) carries increased risk of type 2 diabetes, hypertension, dyslipidaemia, coronary artery disease, and some cancers. Obesity Class I–III progressively increases these risks: Class III obesity (BMI ≥ 40) roughly triples the risk of type 2 diabetes and doubles cardiovascular mortality compared with normal weight. Underweight (BMI < 18.5) is associated with malnutrition, immune impairment, osteoporosis, and elevated mortality particularly from respiratory and digestive diseases. The Global Burden of Disease Study (2015) identified high BMI as the fifth leading risk factor for global mortality, accounting for approximately 4 million deaths per year. Source: GBD 2015 Obesity Collaborators. NEJM 2017; 377:13–27.
Kurzreferenzkarte
BMI Quick Reference
Kurzreferenz • BMI-Rechner
Metric: BMI = kg / m² | Imperial: BMI = 703 × lb / in²Gültiger Bereich: Height: 50–250 cm (2–8 ft) | Weight: 10–500 kg (22–1100 lb) | Age: adults 18+
Häufige Werte
⚠ Achtung
- •BMI categories are validated only for adults (age 18+); use BMI-for-age percentiles for children.
- •Do not use BMI alone during pregnancy — maternal weight gain has separate guidelines.
- •Highly muscular individuals (athletes, bodybuilders) may be falsely classified as Overweight or Obese.
- •BMI alone should never drive clinical decisions — combine with waist circumference, blood tests, and clinical examination.
Profi-Tipps
- →Weigh yourself in the morning after using the bathroom and before eating for the most consistent results.
- →Measure height without shoes; even 1 cm of error shifts BMI by about 0.3 points at average stature.
- →Track BMI monthly rather than daily — daily weight fluctuates 1–3 kg due to hydration and food volume.
- →For Asian ancestry, consider the 23/27.5 thresholds discussed with your physician rather than standard 25/30.
FAQ
What is BMI and what does it measure?
BMI (Body Mass Index) is a number derived from your height and weight using the formula BMI = kg / m² (metric) or 703 × lb / in² (imperial). It provides a quick population-level screening estimate of whether a person's weight is in a healthy range. It does not directly measure body fat percentage, muscle mass, or metabolic health, so it should be interpreted alongside other assessments.
What is a healthy BMI range for adults?
The World Health Organization considers a BMI of 18.5 to 24.9 as the 'Normal weight' (healthy) range for adults. BMI below 18.5 is Underweight; 25–29.9 is Overweight; 30–34.9 is Obese Class I; 35–39.9 is Obese Class II; and 40 or above is Obese Class III. Asian-ancestry populations may be advised to use lower thresholds (overweight ≥ 23, obese ≥ 27.5) due to elevated metabolic risk at lower BMI values.
How do I calculate BMI manually?
Metric: Divide your weight in kilograms by your height in metres squared. Example: 70 kg ÷ (1.75 m)² = 70 ÷ 3.0625 = 22.9. Imperial: Multiply your weight in pounds by 703, then divide by your height in inches squared. Example: 154 lb × 703 ÷ 70² = 108,262 ÷ 4,900 = 22.1.
Does BMI apply to children or teenagers?
No — the WHO adult BMI categories (18.5, 25, 30, 40 thresholds) apply only to adults aged 18 and over. For children and teenagers (ages 2–19), the CDC and WHO use BMI-for-age percentiles, which account for the fact that normal BMI changes significantly with age and sex during growth. A BMI at the 85th percentile or above is considered overweight for children; at or above the 95th percentile is obese.
Why can BMI be misleading for athletes or muscular people?
BMI cannot distinguish between fat mass and lean mass. A bodybuilder or elite athlete may have a BMI of 28–30 (classified as Overweight) purely because of high muscle density, with very low body fat. Conversely, a sedentary individual with a BMI of 23 may carry excess visceral fat that BMI does not detect. For athletes, direct body fat measurements such as DEXA scan, hydrostatic weighing, or skinfold callipers provide a more accurate picture.
What is the BMI formula for imperial units?
The imperial BMI formula is BMI = 703 × weight (lb) / height (in)². The factor 703 is a conversion constant that adjusts the lb/in² ratio to be numerically equivalent to kg/m². For example: BMI = 703 × 154 / (70)² = 108,262 / 4,900 = 22.1. Convert height in feet and inches to total inches first (e.g., 5 ft 10 in = 70 in).
How much weight do I need to lose to reach a healthy BMI?
The calculator computes this automatically. The 'Weight to Lose' output is the difference between your current weight and the maximum weight for a BMI of 24.9 at your height. For a person 170 cm tall weighing 85 kg: max healthy weight = 24.9 × (1.70)² = 72.0 kg; weight to lose = 85 − 72.0 = 13.0 kg. If your BMI is already within the normal range, both fields will show zero.
What are the BMI thresholds for Asian populations?
The WHO Western Pacific Regional Office (2000) proposed lower BMI thresholds for Asian populations due to evidence that metabolic complications occur at lower weights in these groups. The recommended cut-offs are: Normal weight 18.5–22.9; At risk (overweight) 23.0–24.9; Obese Class I 25.0–29.9; Obese Class II ≥ 30.0. Some guidelines further use 27.5 as a trigger for obesity intervention. These thresholds are not universally adopted but are used clinically in Singapore, Japan, and several other Asian countries.