BMI Calculator
Your details
Result
Your BMI
- WHO category
- Healthy weight
- Healthy weight for your height
- 56.7 kg – 76.3 kg
- A BMI of 24.5 falls in the "Healthy weight" band on the WHO adult scale.
- BMI is a population screening tool, not a diagnosis. It cannot distinguish muscle from fat, and it is not valid for children, during pregnancy, or for highly muscular people.
WHO BMI categories
The adult classification, with the weight each band corresponds to at your height.
| Category | BMI | Weight at your height |
|---|---|---|
| Severe thinness | Under 16 | Under 49 kg |
| Moderate thinness | 16 – 17 | 49 kg – 52.1 kg |
| Mild thinness | 17 – 18.5 | 52.1 kg – 56.7 kg |
| Healthy weight | 18.5 – 25 | 56.7 kg – 76.6 kg |
| Overweight | 25 – 30 | 76.6 kg – 91.9 kg |
| Obesity class I | 30 – 35 | 91.9 kg – 107.2 kg |
| Obesity class II | 35 – 40 | 107.2 kg – 122.5 kg |
| Obesity class III | 40 and above | 122.5 kg and above |
How is BMI calculated?
BMI is calculated by dividing weight in kilograms by height in metres squared. Someone weighing 75kg at 1.75m has a BMI of 75 ÷ (1.75 × 1.75) = 24.5. In imperial units the formula is 703 times weight in pounds divided by height in inches squared.
BMI = weight (kg) ÷ height (m)² BMI = 703 × weight (lb) ÷ height (in)²- weight
- Body mass in kilograms, or pounds for the imperial form
- height
- Standing height in metres, or inches for the imperial form
- 703
- The conversion constant that makes the imperial form return the same number
BMI divides weight by the square of height, which adjusts for the fact that taller people are heavier without being proportionally larger. The index was devised by Adolphe Quetelet in the 1830s as a population statistic, and that origin explains its main limitation: it was never designed to assess an individual. Because it uses only two numbers it cannot distinguish muscle from fat, so a muscular athlete and a sedentary person of the same height and weight receive the same score. It also says nothing about where fat is carried, which matters more for metabolic risk than the total. Waist circumference and waist-to-height ratio are better single measures of that risk, and a ratio above 0.5 is a widely used threshold. The imperial constant of 703 exists purely to reconcile units — it is 2.20462 pounds per kilogram divided by 0.0254 metres per inch squared.
- Measure your weight in kilograms and height in metres.
- Multiply your height by itself to square it.
- Divide your weight by that squared height.
- Compare the result against the WHO bands.
- For imperial units, use 703 × pounds ÷ inches squared instead.
Worked example: Someone weighing 75kg at 175cm tall
Someone weighing 75kg at 175cm tall
Convert the height to metres: 175cm is 1.75m. Square it: 1.75 × 1.75 = 3.0625. Divide the weight by that: 75 ÷ 3.0625 = 24.49, which rounds to a BMI of 24.5. That sits in the WHO healthy-weight band of 18.5 to 24.9, though close to its upper edge — gaining two kilograms would move it to 25.1 and into the overweight band. Working backwards gives the healthy weight range for this height directly: 18.5 × 3.0625 = 56.7kg at the lower end and 24.9 × 3.0625 = 76.3kg at the upper. The imperial route reaches the same place: 75kg is 165.3lb and 1.75m is 68.9in, so 703 × 165.3 ÷ (68.9 × 68.9) = 24.5. A difference in the first decimal between calculators is usually rounding in the unit conversion rather than an error.
What each bmi input means
- Units
- Which measurement system your figures are in. The inputs below change to match.
- Weight
- Your weight in kilograms. Weigh yourself in the morning for consistency.
- Height
- Your standing height in centimetres, without shoes.
- Weight
- Your weight in pounds.
- Height (feet)
- The feet part of your height.
- Height (inches)
- The remaining inches on top of the feet.
What this bmi does not account for
- BMI cannot distinguish muscle from fat. Athletes and heavily muscled people are routinely classified as overweight or obese despite low body fat.
- It is not valid for anyone under 20. Children and teenagers are assessed on BMI-for-age percentile charts, because healthy body composition changes substantially with growth.
- It is not valid during pregnancy, and pre-pregnancy BMI is used instead for weight-gain guidance.
- It says nothing about fat distribution. Abdominal fat carries higher metabolic risk than the same amount elsewhere, and BMI is blind to the difference.
- Thresholds differ by population. Several health bodies apply lower cut-offs for people of South Asian, Chinese and Japanese descent — commonly 23 for overweight and 27.5 for obesity — because cardiometabolic risk rises at a lower BMI.
- It loses accuracy in older adults, where muscle mass declines while weight may not, and for anyone with a limb amputation or significant fluid retention.
Frequently asked questions
What is a healthy BMI?
The WHO defines 18.5 to 24.9 as healthy for adults. Below 18.5 is underweight, 25 to 29.9 overweight, and 30 or above obesity. Some health bodies use lower thresholds for people of South and East Asian descent.
How do I calculate BMI manually?
Divide your weight in kilograms by your height in metres squared. At 75kg and 1.75m: 1.75² = 3.0625, and 75 ÷ 3.0625 = 24.5. In imperial units, multiply pounds by 703 and divide by inches squared.
Is BMI accurate?
It is useful as a population screen and poor as an individual diagnosis. Because it uses only height and weight it cannot separate muscle from fat, and it ignores where fat is carried, which matters more for health risk.
Does BMI work for athletes?
Not well. Muscle is denser than fat, so a muscular athlete often scores in the overweight or obese range despite very low body fat. Body fat percentage or waist-to-height ratio is far more informative for that group.
What is a better measure than BMI?
Waist-to-height ratio is the most practical alternative, and a ratio above 0.5 is a common risk threshold. Waist circumference and body fat percentage also capture fat distribution, which BMI cannot.
Does BMI work for children?
Not in this form. Children and teenagers use BMI-for-age percentiles that compare them against others of the same age and sex, because healthy body composition changes throughout growth.
Sources and review
“BMI is a simple index of weight-for-height that is commonly used to classify underweight, overweight and obesity in adults.”
A healthy lifestyle — WHO recommendations on body mass index — World Health Organization- About Adult BMI — Centers for Disease Control and Prevention
Last reviewed .