BMI Calculator
Calculate your Body Mass Index from weight and height. Supports metric and imperial units with a colour-coded result and category table.
<18.5 Normal
18.5 Overweight
25 Obese
30+
| Category | BMI Range |
|---|---|
| Underweight | < 18.5 |
| Normal weight | 18.5 – 24.9 |
| Overweight | 25 – 29.9 |
| Obese | ≥ 30 |
BMI Calculator is a fast, browser-based tool that computes your Body Mass Index from your weight and height. It supports both metric (kg and cm) and imperial (lbs, feet, and inches) units, and shows your result alongside a colour-coded gauge and a reference table so you can immediately see which category you fall into. All calculations run in your browser — no data is sent to a server.
Tool interface
The interface has a unit toggle and two input fields:
- Metric mode — enter weight in kilograms and height in centimetres
- Imperial mode — enter weight in pounds and height in feet and inches
After clicking Calculate BMI, the tool displays:
- Your BMI score to one decimal place
- A category label (Underweight, Normal, Overweight, or Obese) with a colour indicator
- An animated gauge showing where your score falls on the BMI scale
- A reference table with all four WHO categories and their ranges, with your category highlighted
BMI formula
Metric:
BMI = weight (kg) / height (m)²Imperial:
BMI = (weight (lbs) / height (in)²) × 703Height in centimetres is converted to metres before the calculation. Height in feet and inches is converted to total inches.
BMI categories (WHO standard)
| Category | BMI Range |
|---|---|
| Underweight | Below 18.5 |
| Normal weight | 18.5 – 24.9 |
| Overweight | 25 – 29.9 |
| Obese | 30 and above |
Common use cases
- Fitness tracking — monitor BMI over time as part of a weight-loss or training programme
- Health screening — quick first check before a medical appointment
- Nutrition planning — a baseline reference when working with a dietitian
- App development — test BMI calculation logic against a reliable reference
FAQ
What is BMI?
BMI stands for Body Mass Index. It is a numerical value derived from your weight and height that is widely used as a screening tool to identify potential weight-related health risks. It does not directly measure body fat, but it correlates with body fat measurements in most adults.
Is BMI accurate for everyone?
BMI is a useful population-level screening tool but has well-known limitations. It does not account for muscle mass, bone density, age, sex, or ethnic background. Athletes with high muscle mass may be classified as overweight when they are not. Always consult a healthcare professional for a full health assessment.
What is a healthy BMI?
According to the World Health Organization (WHO), a BMI between 18.5 and 24.9 is considered normal weight. Values below 18.5 indicate underweight, 25–29.9 indicates overweight, and 30 or above indicates obesity.
How do I convert my height for the imperial formula?
Multiply feet by 12 and add the remaining inches to get the total height in inches. For example, 5 feet 9 inches equals (5 × 12) + 9 = 69 inches. The calculator does this conversion automatically when you use the Imperial mode.
Can I use this for children?
This calculator uses the standard adult BMI formula. BMI interpretation for children and teenagers uses age- and sex-specific percentiles, which are different from adult thresholds. For children, consult a paediatrician or use a dedicated child BMI tool.