BMI Calculator
Calculate your Body Mass Index quickly to see if you are at a healthy weight.
Your BMI Result
22.9
Great job! You are within the healthy weight range.
About BMI Calculator
What is the Body Mass Index (BMI)?
The Body Mass Index (BMI) is a standardized, universally recognized health metric that utilizes your height and weight to estimate your total body fat. It was developed in the 19th century by Adolphe Quetelet and has since become the primary screening tool used by the World Health Organization (WHO), doctors, and health professionals to categorize weight ranges that may lead to health problems.
The BMI Formula
The mathematical formula for calculating BMI is universally defined as weight in kilograms divided by height in meters squared (BMI = kg/m²). For individuals using the imperial system, the formula is modified to (lbs / in²) × 703. Our calculator handles both metric and imperial math automatically in the background.
Understanding the BMI Categories:
- Underweight (Below 18.5): Indicates you may be malnourished or have a fast metabolism. A doctor might suggest a weight gain plan.
- Normal Weight (18.5 – 24.9): The optimal healthy range for the average adult. Associated with the lowest risk of cardiovascular disease.
- Overweight (25.0 – 29.9): Indicates excess body weight. Lifestyle changes like diet and exercise are often recommended.
- Obese (30.0 and above): Indicates a high amount of body fat, which significantly increases the risk of serious health conditions like type 2 diabetes, high blood pressure, and heart disease.
The thresholds above are not universal — ethnicity shifts them
The 25 and 30 cut-offs were derived from predominantly European populations, and the WHO has since acknowledged that they under-flag risk for people of Asian descent, who tend to carry more visceral fat and develop type 2 diabetes and hypertension at lower BMI values. The WHO Expert Consultation therefore describes additional public-health action points at 23 (increased risk) and 27.5 (high risk) for Asian populations, and several countries — Singapore, Japan, China and India among them — have adopted lower national thresholds accordingly. If that applies to you, read a BMI of 24 as a prompt to look closer rather than as an all-clear. This calculator reports the standard WHO figures; the interpretation is yours to adjust.
A better second number: waist-to-height ratio
BMI's single biggest blind spot is that it has no idea where your weight sits, and abdominal fat is what actually drives metabolic risk. The cheapest fix takes a tape measure: divide your waist circumference by your height, in whatever unit you like, since the ratio cancels the units out. Below 0.5is the widely used rule-of-thumb target — “keep your waist to less than half your height.” A normal BMI paired with a ratio above 0.5 is exactly the combination BMI alone would have missed. You can work the division out with our percentage calculator.
Where the mysterious 703 comes from
The imperial formula's magic number is not arbitrary — it is pure unit conversion folded into a single constant. One pound is 0.453592 kg and one inch is 0.0254 m, so converting lb/in² into kg/m² means multiplying by 0.453592 ÷ 0.0254², which works out to roughly 703. That is the entire mystery. If you would rather convert your own height and weight into metric first and use the clean kg/m² formula, our lb to kg and feet to meters converters will do it exactly.
This tool is a screening aid for general information only. It is not a medical diagnosis and does not replace assessment by a qualified healthcare professional.
Frequently Asked Questions
Is BMI an accurate measure of health?
BMI is an excellent, quick screening tool for general populations, but it has clinical limitations. It does not directly measure body fat percentage, nor does it account for where the fat is stored (visceral vs. subcutaneous fat). It also cannot distinguish between fat mass, muscle mass, and bone density.
Why is BMI inaccurate for bodybuilders and athletes?
Muscle tissue is significantly denser and heavier than fat tissue. Professional athletes, bodybuilders, and fitness enthusiasts often have high body weights due to heavy muscle mass, which can cause their BMI to categorize them as 'Overweight' or 'Obese' despite having very low body fat percentages.
Are these categories applicable to children and teenagers?
No. The standard BMI categories (18.5 to 24.9) are strictly for adults aged 20 and older. For children and teens (ages 2 to 19), BMI must be calculated and then plotted on a CDC growth chart to obtain a percentile ranking relative to other children of the same age and sex.
Should the BMI cut-offs be lower for people of Asian descent?
Many health authorities say yes. The standard 25 and 30 thresholds came from largely European data, and the WHO Expert Consultation noted that Asian populations tend to develop type 2 diabetes and cardiovascular disease at lower BMI values, proposing additional public-health action points at 23 and 27.5. Singapore, Japan, China and India use lower national thresholds as a result. This calculator shows the standard WHO figures, so adjust your reading of them accordingly.
Where does the 703 in the imperial BMI formula come from?
It is a unit-conversion constant, not a fudge factor. A pound is 0.453592 kg and an inch is 0.0254 m, so converting lb/in² into kg/m² means multiplying by 0.453592 ÷ 0.0254², which comes to approximately 703. Using metric inputs directly avoids the constant entirely.
What is a better metric to check alongside BMI?
Waist-to-height ratio. Divide your waist circumference by your height in the same unit — the units cancel, so it works in inches or centimetres. Below 0.5 is the common target, which is why it is often phrased as keeping your waist under half your height. It captures abdominal fat, which is the thing BMI is structurally unable to see.
What should I do if my BMI is high?
A high BMI should be treated as an early warning sign, not a definitive diagnosis. You should consult with a certified healthcare provider or a registered dietitian who can perform more comprehensive assessments, such as skinfold thickness measurements, diet evaluations, and blood tests.