BMI Calculator
Calculate your Body Mass Index using metric or imperial units. See your BMI category, healthy weight range, BMI prime, weight difference, formula, and simple guidance for adults.
Enter your height and weight
Choose your unit system, then enter weight and height. Results update when you calculate.
Adult BMI categories
What Is BMI?
BMI stands for Body Mass Index. It is a simple calculation that uses your height and weight to estimate whether your body weight is low, within the normal adult range, above the normal range, or in the obesity range. BMI is widely used because it is fast, easy to calculate, and useful for population-level screening.
BMI is not a direct measurement of body fat. It does not know how much of your body weight is muscle, fat, bone, or water. That means two people can have the same BMI but very different body composition. Still, BMI can be a useful first step for understanding general weight status.
This calculator is built for adults. For children and teenagers, BMI should be interpreted using BMI-for-age percentiles because healthy ranges change during growth. For medical decisions, BMI should be considered together with waist measurement, health history, activity level, blood tests, and professional advice.
BMI Formula
The BMI formula depends on the unit system. In metric mode, weight is measured in kilograms and height is converted from centimeters to meters. In imperial mode, weight is measured in pounds and height is measured in inches.
Worked Examples
Example 1: Metric BMI
If your weight is 70 kg and your height is 175 cm, first convert height to meters: 175 cm = 1.75 m. Then calculate 70 ÷ 1.75². The result is about 22.9, which falls in the normal adult BMI range.
Example 2: Imperial BMI
If your weight is 154 lb and your height is 5 ft 9 in, total height is 69 inches. The formula is 703 × 154 ÷ 69². The result is about 22.7, which is also in the normal adult BMI range.
Example 3: Healthy weight range
The calculator estimates the weight range that would place your BMI between 18.5 and 24.9 for your height. This is a general adult screening range, not a personal medical target.
Example 4: BMI prime
BMI prime compares your BMI with 25. A BMI of 22 has a BMI prime of 0.88. A BMI of 30 has a BMI prime of 1.20. This helps show how far BMI is from the upper end of the normal adult range.
How to Use This BMI Calculator
Select metric or imperial units.
Enter your weight in kg or pounds.
Enter your height in cm or feet and inches.
Calculate and review BMI, category, healthy range, and formula.
Frequently Asked Questions
What is BMI?
BMI stands for Body Mass Index. It is a screening number calculated from height and weight. For adults, it is commonly used to estimate whether a person is underweight, in the normal weight range, overweight, or in the obesity range.
How is BMI calculated?
In metric units, BMI equals weight in kilograms divided by height in meters squared. In imperial units, BMI equals 703 multiplied by weight in pounds divided by height in inches squared.
What is a healthy BMI range?
For most adults, a BMI from 18.5 to 24.9 is commonly considered the normal or healthy weight range. A BMI below 18.5 is underweight, 25 to 29.9 is overweight, and 30 or above is in the obesity range.
Is BMI accurate for everyone?
No. BMI is useful as a quick screening tool, but it does not distinguish between muscle, fat, bone, or body shape. Athletes, pregnant people, older adults, children, and people with unusual muscle mass may need other measurements.
Can children use this BMI calculator?
This calculator uses adult BMI categories. Children and teenagers need BMI-for-age percentiles because healthy ranges change with age and sex during growth.
What is BMI prime?
BMI prime compares your BMI with 25, the upper end of the normal adult BMI range. A value below 1 means BMI is below 25, while a value above 1 means BMI is above 25.