Body Mass Index (BMI) Calculator

Use our accurate BMI calculator to check your weight status in seconds. Body Mass Index provides a quick, reliable screening number used by healthcare providers worldwide to evaluate body composition and weight-related health risks.

What is Body Mass Index (BMI)?

Body Mass Index (BMI) is a simple numerical score derived from an adult's weight and height. It serves as an accessible screening tool to identify whether someone is underweight, normal weight, overweight, or obese. While BMI does not measure body fat percentage directly, research shows it correlates closely with direct fat-measuring methods.

How This Calculator Works

Our tool handles both standard US Imperial units (pounds and inches) and Metric measurements (kilograms and meters or centimeters). Simply enter your height and weight into the form. The calculator processes your numbers instantly against standard CDC brackets, showing your current category alongside practical weight ranges for your height.

The BMI Formula & How to Calculate Manually

If you want to know how to calculate my BMI manually, you can run the numbers with basic math using either system:

1. US Imperial Unit Formula (lbs & inches)

BMI = [Weight (lbs) / Height (inches)²] × 703

2. Standard Metric Formula (kg & meters)

BMI = Weight (kg) / Height (meters)²

Manual Calculation Example:

For a person weighing 165 lbs who stands 5 feet 10 inches tall (70 inches):

Square height: 70 × 70 = 4,900
Divide weight by squared height: 165 / 4,900 = 0.03367
Multiply by conversion factor: 0.03367 × 703 = 23.67 BMI (Normal weight)

Healthy BMI Range for Adults

Standard clinical cutoffs establish the following weight categories for adult men and women:

BMI Range	Weight Status Classification
Below 18.5	Underweight
18.5 – 24.9	Normal / Healthy Weight
25.0 – 29.9	Overweight
30.0 and Above	Obese

Understanding BMI by Age and Sex

When searching for a BMI calculator for women or a BMI calculator for men by age, keep in mind that the base mathematical formula remains identical for all adults. However, physiological interpretation often differs:

Biological Sex: Women naturally carry more essential body fat than men at the exact same BMI score.
Age: Older adults naturally lose lean muscle and gain fat tissue. For seniors over 65, several studies suggest a slightly higher BMI (around 25 to 27) correlates with better bone density and recovery from illness.
Body Composition: A BMI reading does not measure waist circumference or visceral fat. Comparing your BMI alongside your waist-to-height ratio provides a more comprehensive health picture.

Frequently Asked Questions

What is a healthy BMI?

For adults 20 and older, a healthy BMI is between 18.5 and 24.9. A score below 18.5 is considered underweight, 25.0 to 29.9 falls into the overweight range, and 30.0 or higher indicates obesity based on standard CDC and WHO guidelines.

How do you calculate BMI by hand?

To calculate BMI by hand using pounds and inches, divide your weight in pounds by your height in inches squared, then multiply by 703. For metric units, divide your weight in kilograms by your height in meters squared.

What is the BMI formula?

The imperial BMI formula is BMI = [Weight (lbs) / Height (inches)²] × 703. The metric formula is BMI = Weight (kg) / Height (meters)².

Is BMI accurate for muscular people?

No. BMI does not distinguish between lean muscle and fat mass. Because dense muscle tissue adds weight without increasing body fat, strength athletes and bodybuilders often score in the overweight or obese range despite low body fat percentages. In these cases, tools like waist-to-height ratio or direct body fat percentage measurements give a more accurate picture.