BMI Calculator
Calculate your Body Mass Index in metric or imperial units and find your healthy weight range.
BMI Categories (WHO standard)
| Category | BMI Range | Health Risk |
|---|---|---|
| Underweight | < 18.5 | Increased risk |
| Normal weight | 18.5 – 24.9 | Low risk |
| Overweight | 25.0 – 29.9 | Increased risk |
| Obese Class I | 30.0 – 34.9 | High risk |
| Obese Class II | 35.0 – 39.9 | Very high risk |
| Obese Class III | ≥ 40.0 | Extremely high risk |
About BMI
Body Mass Index (BMI) is calculated as weight in kilograms divided by height in metres squared (kg/m²). It was developed by Belgian statistician Adolphe Quetelet in the 1830s and remains the most widely used quick screening metric for weight categories.
What is a healthy BMI?
The World Health Organisation defines a healthy BMI range as 18.5 to 24.9 for adults. Below 18.5 is considered underweight and 25 or above is overweight.
Is BMI accurate?
BMI does not distinguish between muscle and fat mass, so very muscular people may be classified as overweight. It also does not account for age, sex, ethnicity or body composition. Use it as a general guide only.
What is the BMI formula?
BMI = weight (kg) ÷ height² (m). For imperial: BMI = 703 × weight (lbs) ÷ height² (inches).
About the BMI Calculator
Our free BMI calculator computes your Body Mass Index from your height and weight, and shows where your result falls on the standard BMI scale. BMI is a widely used screening tool that gives a quick indication of whether a person's weight is in a healthy range relative to their height. Both metric (kg/cm) and imperial (lb/ft-in) units are supported.
Important: BMI is a population-level screening tool, not a diagnostic measure. It does not account for muscle mass, bone density, age, sex, or ethnic background. Always consult a healthcare professional for a full assessment of your health.
BMI Categories
- Under 18.5 — Underweight. May indicate nutritional deficiency or other health concerns.
- 18.5 – 24.9 — Normal weight. Associated with the lowest health risks in large population studies.
- 25.0 – 29.9 — Overweight. Slightly elevated risk for certain conditions; not automatically a health problem.
- 30.0 – 34.9 — Obese Class I. Associated with increased health risks.
- 35.0 – 39.9 — Obese Class II. Significantly increased health risks.
- 40.0 and above — Obese Class III (severe obesity). Highest associated health risks.
How BMI Is Calculated
BMI = weight in kilograms ÷ (height in metres)². For example: a person who weighs 70 kg and is 1.75 m tall has a BMI of 70 ÷ (1.75²) = 70 ÷ 3.0625 = 22.9, which falls in the normal weight range.
In imperial units: BMI = (weight in pounds × 703) ÷ (height in inches)².
Limitations of BMI
BMI is a simple, inexpensive screening tool but has known limitations. Athletes with high muscle mass may have a BMI in the overweight range despite having very low body fat. Elderly individuals may have a normal BMI while having lost significant muscle mass (sarcopenia). Differences in body composition between ethnic groups also mean that BMI thresholds may not be equally appropriate for all populations. Medical organisations increasingly recommend BMI be used alongside other measures such as waist circumference, waist-to-hip ratio, and body fat percentage.
Frequently Asked Questions
What is a healthy BMI?
The World Health Organisation defines a healthy BMI as 18.5 to 24.9 for adults. However, optimal ranges may differ for children, the elderly, and different ethnic populations.
Is BMI accurate for athletes?
No. Athletes with high muscle mass often have a BMI in the overweight or obese range despite having low body fat. For athletes, direct body composition measurement (DEXA scan, hydrostatic weighing) is more informative.
Does BMI apply to children?
For children and teens, BMI is age- and sex-specific (BMI-for-age). The thresholds are different from adult BMI ranges. Paediatric BMI should always be assessed by a healthcare provider.
Can I use pounds and inches?
Yes. Toggle to imperial units and enter your weight in pounds and height in feet and inches.