BMI Calculator
Calculate your Body Mass Index based on your height and weight
Quick Answer
A healthy BMI is between 18.5 and 24.9. Enter your height and weight below to find yours in under 30 seconds.
BMI Calculator: formula, worked examples and limitations
A complete reference answer — readable without using the calculator.
Definition
Body Mass Index (BMI) is a screening index that relates body weight to height. It was introduced by Adolphe Quetelet in the 1830s and is used by the World Health Organization to classify weight status at population level.
What it measures
BMI measures weight relative to height. It does not measure body fat, fat distribution or muscle mass, so it is a screening indicator rather than a diagnosis.
Formula
- Metric: BMI = weight (kg) ÷ height (m)²
- Imperial: BMI = 703 × weight (lb) ÷ height (in)²
Worked examples
Computed with the same engine as the calculator above.
70 kg, 175 cm
Inputs: weight = 70 kg, height = 175 cm (1.75 m)
70 ÷ 1.75² = 22.9
BMI 22.9 — Normal weight
90 kg, 175 cm
Inputs: weight = 90 kg, height = 175 cm (1.75 m)
90 ÷ 1.75² = 29.4
BMI 29.4 — Overweight
55 kg, 168 cm
Inputs: weight = 55 kg, height = 168 cm (1.68 m)
55 ÷ 1.68² = 19.5
BMI 19.5 — Normal weight
| BMI range (kg/m²) | Classification |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Normal weight |
| 25.0 – 29.9 | Overweight |
| 30.0 and above | Obese |
| Weight | Height | BMI | Category |
|---|---|---|---|
| 70 kg | 175 cm | 22.9 | Normal weight |
| 90 kg | 175 cm | 29.4 | Overweight |
| 55 kg | 168 cm | 19.5 | Normal weight |
Method
The calculator converts imperial input to metric (1 lb = 0.453592 kg, 1 in = 2.54 cm), applies the metric BMI formula, and classifies the result against the WHO adult thresholds.
Limitations
- BMI cannot distinguish muscle from fat; muscular athletes are frequently classified as overweight.
- It ignores fat distribution — visceral fat carries higher risk than subcutaneous fat at the same BMI.
- Risk thresholds differ by ethnicity; elevated metabolic risk starts around BMI 23 in South Asian populations.
- Not valid for children, adolescents, pregnant people, or adults with large amounts of oedema.
Rounding rules
BMI is displayed with one decimal. Categories are applied to the unrounded value.
Evidence level
Well established. BMI and its cut-offs are defined by the WHO and used in clinical and epidemiological practice. BMI is a population-level screening index, not a diagnosis or a measure of body fat.
Sources
Method and reference values last reviewed by the SnapBodyCalc editorial team.
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Learn more
Understanding Your BMI and What It Really MeansYour Body Mass Index (BMI) is one of the most commonly used health metrics, but what does it actually tell you? Learn how to interpret your BMI results and understand its limitations.
Read articleRelated Calculators
Frequently Asked Questions
Understanding BMI: Your Complete Guide to Body Mass Index
Body Mass Index (BMI) is one of the most widely used health screening tools in the world. Developed by Belgian mathematician Adolphe Quetelet in the 1830s and adopted by the World Health Organization (WHO), BMI provides a quick, cost-free method to categorize individuals based on body weight relative to height. While not a direct measure of body fat, BMI serves as a valuable first step in identifying potential weight-related health risks and has been validated across hundreds of population-level studies.
How BMI is Calculated
The BMI formula is straightforward: weight in kilograms divided by height in meters squared (kg/m²). For imperial units, the formula is: (weight in pounds × 703) ÷ (height in inches)². Our calculator handles these conversions automatically, giving you instant results in either metric or imperial units. A person weighing 75 kg at 1.78 m tall, for example, would have a BMI of 23.7 — within the healthy range.
BMI Categories Explained
The WHO classifies BMI into four primary categories. Underweight (below 18.5) may indicate nutritional deficiencies, eating disorders, or underlying health conditions and is associated with increased risk of osteoporosis, fertility issues, and weakened immunity. Normal weight (18.5–24.9) is associated with the lowest overall health risks and optimal metabolic function. Overweight (25–29.9) indicates elevated risk for cardiovascular disease, type 2 diabetes, and certain cancers. Obese (30 and above) carries significantly increased health risks, with further subdivisions: Class I (30–34.9), Class II (35–39.9), and Class III or "severe" obesity (40+).
Limitations of BMI
While BMI is a valuable screening tool, it has well-documented limitations. It doesn't distinguish between muscle and fat mass — a muscular athlete might be classified as "overweight" despite having 10% body fat. It doesn't account for fat distribution (visceral vs. subcutaneous fat), which significantly affects health risk. Age-related muscle loss means older adults may have a "normal" BMI but carry excess body fat. Ethnic variations also matter: South Asian populations face elevated metabolic risk at lower BMI thresholds (23+), while some Pacific Islander populations may be healthy at higher BMIs.
BMI vs. Other Body Composition Metrics
For a more complete health picture, BMI should be used alongside other metrics. Our Body Fat Calculator estimates actual fat percentage, distinguishing between muscle and fat mass. The Waist-to-Hip Ratio Calculator reveals dangerous visceral fat accumulation that BMI misses entirely. Our Lean Body Mass Calculator shows how much of your weight is metabolically active tissue. Together, these metrics provide a far richer health assessment than BMI alone.
BMI and Health Risk: What the Research Shows
Large-scale epidemiological studies involving millions of participants consistently show a J-shaped relationship between BMI and mortality: both very low (under 18.5) and high (over 30) BMIs are associated with increased health risks. The lowest mortality risk is typically observed in the BMI range of 20–25. However, fitness level modifies this relationship significantly — a fit individual with a BMI of 27 may have lower health risks than a sedentary person with a BMI of 22.
Using BMI for Weight Management Goals
If your BMI falls outside the healthy range, our suite of calculators can help you take action. Our Calorie Calculator provides personalized daily calorie targets for weight loss or gain. The TDEE Calculator reveals your total daily energy expenditure. For sustainable weight change, aim for 0.5–1 kg per week, which typically requires a 500–1000 calorie daily deficit or surplus.
BMI for Children and Adolescents
Note that our calculator is designed for adults aged 18 and older. Children and adolescents use age- and sex-specific BMI percentile charts because their body composition changes dramatically during growth. A child's BMI is compared to others of the same age and sex rather than to fixed thresholds.
Privacy and Accuracy
SnapBodyCalc calculates everything directly in your browser. Your weight, height, and results are never sent to any server or stored anywhere. We believe health data should remain private, which is why we've built all our calculators with privacy as a core principle. Use our tools confidently, knowing your information stays with you. Analytics and web fonts still make standard requests that include your IP address and the page URL — but never your measurements.