Want to check your BMI quickly? A BMI calculator uses your height and weight to calculate your Body Mass Index. You enter your details, and the tool gives you a BMI number along with the standard BMI category for adults.

The calculation only takes a few seconds.

What is BMI?

BMI stands for Body Mass Index. It's a number calculated from your weight and height.

For adults, BMI is commonly used as a simple screening measurement. Doctors and other health professionals may use it alongside other information when looking at a person's general health.

The basic formula is:

BMI = weight ÷ height²

When using kilograms and meters, the formula is easy to calculate.

For example, if someone weighs 70 kg and is 1.75 meters tall:

BMI = 70 ÷ (1.75 × 1.75)
BMI = 22.86

The BMI is about 22.9.

A calculator saves you from doing the math yourself.

How does a BMI calculator work?

A BMI calculator needs 2 pieces of information:

Your weight
Your height
You can usually enter weight in kilograms or pounds and height in centimeters, meters, feet, or inches.

The tool converts the measurements when needed, applies the BMI formula, and displays the result.

For example, you could enter:

Weight: 70 kg
Height: 175 cm

The calculator converts 175 cm to 1.75 meters and calculates the BMI.

Adult BMI categories

For adults, the commonly used BMI categories are:

BMI                 Category

Below 18.5             Underweight
18.5 to 24.9            Healthy weight
25.0 to 29              Overweight
30.0 or higher        Obesity

These ranges are commonly used for adults aged 20 and older.

A BMI number gives you a general screening result. It doesn't tell you everything about your health.

Why use a BMI calculator?

Doing the calculation manually is possible, but there's plenty of room for a small mistake.

You might enter your height in centimeters while using a formula that expects meters. Or you might forget to square the height.

A calculator handles those steps for you.

It's useful when you're checking your BMI during a fitness program, keeping a personal record, or simply trying to understand how BMI is calculated.

BMI calculator for men and women

The standard adult BMI formula is the same for men and women.

For example, a 30-year-old man weighing 80 kg at 1.80 meters has:

80 ÷ (1.80 × 1.80) = 24.69

A 30-year-old woman with the same height and weight would also have a BMI of 24.69.

BMI itself doesn't change based on sex. The interpretation of an individual person's health can involve many other factors.

BMI calculator for children

Children and teenagers need a different approach.

For people aged 2 to 19, BMI is usually interpreted using BMI-for-age percentiles, which take age and sex into account.

So an adult BMI category shouldn't be used to judge a child's weight status.

If you're checking BMI for a child or teenager, use a calculator designed specifically for their age group and discuss the result with a pediatrician or other qualified health professional.

BMI calculator for adults

Adult BMI calculations are generally simpler.

You enter your weight and height, and the calculator returns the BMI value. The result can then be compared with the standard adult BMI ranges.

For example:

Weight: 90 kg
Height: 1.80 m

BMI = 90 ÷ (1.80 × 1.80)
BMI = 27.78

A BMI of 27.8 falls within the overweight range for adults.

The number is a screening measurement, so it should be viewed alongside other information about your health.

BMI and weight

BMI is based on weight and height, so changes in either measurement will change the result.

If your height stays the same and your weight increases, your BMI increases. If your weight decreases, your BMI decreases.

For example, at a height of 1.75 meters:

60 kg = BMI 19.59
70 kg = BMI 22.86
80 kg = BMI 26.12
90 kg = BMI 29.39

Small changes in weight can therefore move the BMI number up or down.

BMI doesn't measure body fat directly

BMI uses only height and weight.

It doesn't directly measure body fat, muscle mass, bone density, or where fat is stored in the body.

That matters because 2 people with the same BMI can have very different body compositions.

For example, someone who does a lot of strength training may have more muscle mass than another person of the same height and weight.

So BMI works best as a basic screening number rather than a complete picture of someone's health.

BMI calculator in pounds and inches

You can also calculate BMI using pounds and inches.

The formula is:

BMI = (weight in pounds × 703) ÷ height in inches²

For example, someone who weighs 154 lb and is 68 inches tall:

BMI = (154 × 703) ÷ (68 × 68)
BMI ≈ 23.39

A calculator can handle the conversion automatically if you prefer entering your measurements in pounds and inches.

Metric BMI calculator

The metric method uses kilograms and meters:

BMI = weight in kg ÷ height in meters²

Example:

Weight: 75 kg
Height: 1.75 m

BMI = 75 ÷ 3.0625
BMI ≈ 24.49

This method is common in countries that use the metric system.

BMI calculator with age

Age matters when interpreting BMI.

For adults, the standard BMI categories are generally used from age 20 onward. Children and teenagers are assessed differently because their bodies are still growing.

Older adults can also have different health considerations, including changes in muscle mass and body composition.

So the BMI number alone shouldn't be used to make a health decision.

BMI and fitness

People often use BMI calculators when starting a fitness or weight-management routine.

You can record your BMI over time and compare changes in your weight and height measurements.

But a single BMI result doesn't tell you whether a particular diet or exercise program is appropriate for you.

Your activity level, diet, medical history, medications, muscle mass, and other factors can matter too.

How to use a BMI calculator

Using the tool is simple.

Step 1: Enter your weight

Choose kilograms or pounds and enter your current weight.

Step 2: Enter your height

Choose centimeters, meters, feet, or inches, depending on what the calculator supports.

Step 3: Calculate

Click the calculate button.

The tool returns your BMI number and, for adults, the corresponding standard BMI category.

Step 4: Understand the result

Use the result as a general screening measurement. If you're concerned about your weight or health, talk with a qualified health professional who can consider your full situation.

BMI calculator FAQs

What is a normal BMI?

For adults, a BMI from 18.5 to 24.9 is commonly classified as the healthy-weight range.

The term "normal" can be misleading because BMI is only one measurement.

What BMI is considered overweight?

For adults, a BMI from 25.0 to 29.9 is commonly classified as overweight.

What BMI is considered obesity?

For adults, a BMI of 30.0 or higher falls within the obesity category.

Is BMI the same for men and women?

The BMI formula is the same for adult men and women.

Can BMI be used for children?

Children and teenagers require BMI-for-age calculations using age and sex-specific growth charts.

Does BMI measure body fat?

No. BMI is calculated from height and weight. It doesn't directly measure body fat.

Can athletes have a high BMI?

Yes. Higher muscle mass can increase body weight and therefore BMI. That's one reason BMI shouldn't be viewed as a complete measurement of body composition.

Check your BMI in seconds

A BMI calculator makes the basic calculation quick.

Enter your height and weight, check the number, and compare it with the appropriate adult BMI range if you're 20 or older.

Remember what the number can tell you. BMI is a screening tool, and your overall health involves much more than a single calculation.