Free Online BMI Calculator

Use this Free Online BMI Calculator to check your Body Mass Index in just a few seconds. Enter your weight, height, and age, and the tool instantly tells you whether you fall into the underweight, normal, overweight, or obese category. It works as a simple BMI calculator online for adults, teenagers, and children, and supports both men and women.

The tool uses the standard BMI calculator formula used worldwide and also functions as a quick BMI converter kg / lb, automatically converting pounds to kilograms when needed.

BMI Calculator

Age Weight

Height (ft & in)

How to Use the BMI Calculator in 3 Simple Steps

Enter Your Weight

Add your weight in kilograms, or switch to pounds if that’s easier. The tool automatically converts lb → kg to make sure your BMI is calculated correctly.

Enter Your Height

Type your height in feet and inches. The calculator converts your height into meters and applies the BMI formula:
BMI = weight (kg) ÷ [height (m)]² You don’t need to do any manual calculations.

Click Calculate BMI

Press the button and instantly see: Your BMI value
Your BMI category (underweight, normal, overweight, obese)
A healthy weight range for your height (in kg and lb)
You can adjust values anytime to re-check your BMI.

BMI Calculator & Converter Tool

Q: What is the BMI calculator formula?

BMI = weight (kg) ÷ [height (m)]² If you enter pounds, the BMI speed calculator converts them into kilograms automatically.

The BMI tool at Free Tool Mart is designed for speed and simplicity:

Enter weight in kg or lb → tool converts lb to kg
Enter height in feet + inches → tool converts to meters
Add age → helpful for understanding BMI differently in adults vs teens

So even though the interface is simple, it works as a BMI converter kg/lb, a fast BMI calculator online, and a general body mass index calculator for both men and women.

BMI Categories for Adults (WHO Standards)

BMI Category	BMI Range (kg/m²)
Severe Thinness	< 16
Moderate Thinness	16 – 17
Mild Thinness	17 – 18.5
Normal Range	18.5 – 25
Overweight	25 – 30
Obese Class I	30 – 35
Obese Class II	35 – 40
Obese Class III	> 40

BMI for Children and Teens (CDC Guidelines)

For children and teenagers (ages 2–20), BMI is interpreted differently. While the numerical formula stays the same, the result must be compared to percentiles based on age and gender.

General CDC percentile categories:

Underweight: below 5th percentile
Healthy weight: 5th–85th percentile
At risk of overweight: 85th–95th percentile
Overweight/Obese: above 95th percentile

This Free Tool Mart BMI calculator by age and gender lets you enter age, but medical interpretation for kids and teens should always be done using official growth charts from a healthcare provider.

Example BMI Calculation (Step-by-Step)

Let’s walk through a typical example:

Age: 25
Height: 5 ft 10 in (≈ 1.78 m)
Weight: 160 lb (≈ 72.5 kg)

Convert height:
70 in × 0.0254 ≈ 1.78 m

Apply the formula:
BMI = 72.5 ÷ (1.78²) ≈ 22.9

Result:
BMI ≈ 23 → Normal Range (18.5 – 25)

This is exactly what the Free Online BMI Calculator will show for the same values.

Health Risks of a High BMI

A higher-than-normal BMI may be associated with increased chances of:

High blood pressure
High cholesterol
Type 2 diabetes
Heart disease and stroke
Sleep apnea
Certain cancers
Joint pain and limited mobility
A BMI calculator for men and women provides an early indicator. It is not a diagnosis; consult a professional for personalized guidance.

Health Risks of a Low BMI

A BMI below 18.5 can sometimes be linked with:

Nutrient deficiencies
Lower immunity
Bone weakness (osteoporosis)
Growth issues in teenagers
Fatigue or low energy levels

Use this BMI calculator free online as a starting point, not a medical conclusion.

Limitations of BMI

BMI is helpful, but it does not measure everything. The formula does not consider:

Muscle vs fat
Fat distribution
Bone density
Body frame size
Fitness level or activity level

Adults

BMI may be misleading for:

Older adults (less muscle, more fat)
Athletic individuals (high muscle mass may show as “overweight”)
People with unique body proportions

That’s why BMI should be interpreted alongside other factors like waist size, body fat percentage, and overall lifestyle.

FAQs – Free Online BMI Calculator

How does the Free Online BMI Calculator work?

It uses the standard formula: weight (kg) ÷ height (m)². You enter your weight (kg or lb), height (ft/in), and age, and the tool instantly shows your BMI category.

What is the BMI calculator formula?

BMI = weight (kg) ÷ [height (m)]²
If you enter pounds, the BMI speed calculator converts them into kilograms automatically.

Is this BMI calculator for men and women?

Yes. The formula is the same for both genders. Interpretation may vary slightly based on age, gender, and body type.

Can I use it as a BMI calculator by age and gender?

Yes. Adults use one interpretation; children/teens must use percentile charts for accuracy.

Does this tool work as a BMI converter kg / lb?

Yes. It converts pounds to kilograms internally, so your BMI is always calculated correctly.

What is the normal BMI range?

For adults: