Calculator Use
This body mass index calculator for adults is a professional tool designed to help men and women over the age of 20 determine their body fat based on weight and height. Body Mass Index (BMI) is a widely used screening tool to identify whether an individual is within a healthy weight range or if their weight may pose potential health risks.
By using this calculator, you can quickly switch between the Imperial (US) system and the Metric system to get accurate results. BMI is calculated differently for adults than it is for children and teens, making this specific version essential for adult health assessments.
- Measurement System
- Choose between US Units (lbs, ft, in) or Metric Units (kg, cm).
- Weight
- Enter your current body weight in pounds or kilograms.
- Height
- Enter your total height. In the US system, this is split into feet and inches.
How It Works
When you use the body mass index calculator for adults, the system applies one of two standard mathematical formulas depending on your chosen units. The core concept measures mass relative to height, assuming that as height increases, weight should increase proportionally at a squared rate.
Metric BMI Formula = weight(kg) / [height(m)]2
US Imperial BMI Formula = 703 × weight(lb) / [height(in)]2
- Weight: Measured in kilograms (metric) or pounds (imperial).
- Height: Height is converted to meters (metric) or total inches (imperial).
- The Square: Height is squared because body volume is three-dimensional, but surface area and mass distribution are roughly two-dimensional in terms of vertical proportion.
- Factor 703: Used in the US system to convert lbs/in2 into kg/m2 equivalent values.
BMI Calculation Example
Example: A person weighing 180 lbs who is 5 feet 10 inches tall wants to find their BMI.
Step-by-step solution:
- Weight = 180 lbs
- Height = 5′ 10″ = (5 × 12) + 10 = 70 inches
- Square the Height = 70 × 70 = 4,900
- Calculate = (180 / 4,900) × 703
- Result = 0.03673 × 703 = 25.8
- Category = Overweight (BMI 25.0 – 29.9)
Understanding BMI Categories
According to the World Health Organization (WHO) and the CDC, the following BMI categories apply to adults aged 20 and older:
| BMI Range | Weight Status |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Normal or Healthy Weight |
| 25.0 – 29.9 | Overweight |
| 30.0 and Above | Obese |
Common Questions
Is BMI accurate for athletes?
BMI can sometimes overestimate body fat in athletes or individuals with high muscle mass because muscle is denser than fat. Conversely, it might underestimate body fat in older adults who have lost muscle mass.
Why use BMI if it's not perfect?
While not a direct measure of body fat, BMI is a highly effective, low-cost, and non-invasive screening tool. It correlates strongly with more expensive metabolic and disease-risk assessments across large populations.
Does age matter for BMI in adults?
For adults over 20, the BMI categories remain the same regardless of age or gender. However, healthcare providers often look at BMI in context with other factors like waist circumference and blood pressure for a complete health profile.