How to Calculate BMI: Formula, Examples, Chart, and What Your BMI Means

If you know your height and weight, you can calculate your BMI in just a few steps.

BMI, or Body Mass Index, compares your weight with your height and produces a number that can be used to place an adult into a weight category. The calculation itself is simple, but it is easy to get the wrong answer if you use centimeters incorrectly, forget to square your height, or mix metric and imperial measurements.

The basic formula is:

BMI = Weight ÷ Height²

If you use kilograms and meters, the calculation is straightforward. If you use pounds and inches, you need to multiply by 703.

If you already have your measurements and just want the answer, you can use our BMI Calculator. If you want to understand where the number comes from and what it means, the guide below walks through the calculation from start to finish.

What Is BMI?

BMI stands for Body Mass Index. It is a calculation based on a person’s weight and height.

For adults, BMI is commonly used as a screening measure to identify whether a person’s weight falls within the underweight, healthy-weight, overweight, or obesity categories. It does not directly measure body fat, and a BMI number by itself cannot tell you whether someone is healthy or unhealthy.

The calculation uses only two measurements:

• Weight
• Height

That makes BMI quick to calculate and easy to use when comparing weight relative to height.

However, the number needs some context. Muscle mass, body composition, pregnancy, age, and whether the person is a child or teenager can all affect how BMI should be interpreted.

What Is the BMI Formula?

The formula depends on the units you’re using.

Metric BMI formula

If your weight is in kilograms and your height is in meters:

BMI = weight (kg) ÷ [height (m)]²

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

BMI = 70 ÷ (1.75 × 1.75)

BMI = 70 ÷ 3.0625

BMI = 22.9

So the person’s BMI is approximately 22.9.

The CDC uses this same metric formula for calculating BMI.

BMI formula using pounds and inches

If your weight is in pounds and your height is in inches:

BMI = [weight (lb) ÷ height (in)²] × 703

For example, someone weighing 165 pounds and measuring 69 inches tall would have:

BMI = (165 ÷ 69²) × 703

BMI ≈ 24.4

The number 703 is the conversion factor used in the U.S. customary version of the BMI formula.

How to Calculate BMI in Kilograms and Centimeters

If your measurements are in kilograms and centimeters, you don’t have to convert your weight. You only need to make sure you handle your height correctly.

For example:

Weight = 70 kg
Height = 175 cm

You can first convert the height into meters:

175 cm = 1.75 m

Now square the height:

1.75 × 1.75 = 3.0625

Then divide your weight by that number:

70 ÷ 3.0625 = 22.86

So:

BMI = 22.9

There is also a direct formula for centimeters:

BMI = [Weight (kg) ÷ Height (cm) ÷ Height (cm)] × 10,000

Using the same example:

BMI = [70 ÷ 175 ÷ 175] × 10,000

BMI = 22.86

Both methods produce the same result.

The most common mistake with centimeters

Don’t put 175 directly into the meter-based formula.

This is wrong:

70 ÷ 175²

unless you are using the centimeter version of the formula with the appropriate 10,000 factor.

For the standard metric formula, convert 175 cm to 1.75 m first.

How to Calculate BMI in Pounds and Inches

If your weight is given in pounds and your height is given in feet and inches, there is one extra step: convert your height into total inches.

Suppose someone is:

5 feet 9 inches tall

There are 12 inches in a foot:

5 × 12 = 60 inches

Then add the remaining 9 inches:

60 + 9 = 69 inches

If the person weighs 165 pounds:

BMI = (165 ÷ 69²) × 703

First square the height:

69 × 69 = 4,761

Then:

165 ÷ 4,761 × 703 = 24.4

So the BMI is approximately 24.4.

The important thing to remember is that the imperial formula uses inches, not feet. The standard formula is weight in pounds divided by height in inches squared, multiplied by 703.

A Complete BMI Calculation Example

Let’s put everything together with a metric example.

Suppose you weigh 85 kg and your height is 180 cm.

Step 1: Convert your height

180 cm = 1.80 m

Step 2: Square your height

1.80 × 1.80 = 3.24

Step 3: Divide your weight by your squared height

85 ÷ 3.24 = 26.23

Your BMI

BMI = 26.2

For an adult, a BMI of 26.2 falls within the overweight category under the standard adult BMI ranges.

The calculation itself is complete at this point. What requires more care is interpreting what that number actually means.

What Does Your BMI Mean?

For adults age 20 and older, the standard BMI categories are:

The CDC further divides obesity into three classes:

These ranges are used for adults regardless of age, sex, or race.

One important wording point is worth keeping in mind: a BMI category is not a diagnosis.

For example, saying that a BMI of 27 falls into the adult overweight category is different from saying that the person is unhealthy. BMI is one screening measure and should be considered alongside other information about a person’s health.

BMI Chart for Adults

Here’s the standard adult BMI scale at a glance:

If your BMI is close to one of the boundaries, don’t read too much into a difference of a few tenths. BMI is a screening number, and the result should be considered in the wider context of your health.

What Is a Healthy BMI?

For adults, the standard healthy-weight BMI range is 18.5 to less than 25.

That doesn’t mean that every person within this range has the same body composition or health status. BMI doesn’t distinguish between muscle, fat, bone, or other components of body weight.

It is better to think of the healthy-weight range as a screening reference, rather than a perfect definition of what your individual weight should be.

If you’re trying to work out what weight range corresponds to your height, you can also use our Healthy Weight Calculator to get a height-based estimate.

How Much Should I Weigh for My Height?

You can use the BMI formula in reverse to estimate the weight associated with a particular BMI.

For metric measurements:

Weight = BMI × Height²

Suppose someone is 1.75 meters tall.

Using the lower end of the adult healthy BMI range:

18.5 × 1.75² = 56.7 kg

Using the upper end:

24.9 × 1.75² = 76.3 kg

So, based strictly on the standard adult BMI range, a height of 1.75 m corresponds to approximately 56.7 to 76.3 kg.

That is a mathematical BMI range, not a personal recommendation about what any particular person should weigh.

If you want to estimate a healthy weight range based on height, the Healthy Weight Calculator can do the calculation without requiring you to work through the formula yourself.

How to Calculate If You Are Overweight From BMI

For adults, a BMI from 25 to less than 30 falls into the overweight category. A BMI of 30 or higher falls into the obesity category.

For example:

• BMI 23.4 → Healthy-weight category
• BMI 24.9 → Healthy-weight category
• BMI 25.0 → Overweight category
• BMI 27.6 → Overweight category
• BMI 29.9 → Overweight category
• BMI 30.0 → Obesity category

If you’re specifically trying to determine whether your weight falls within the overweight range based on your height, you can use Overweight Calculator.

Keep in mind that being placed in the overweight BMI category does not, by itself, tell you how much body fat you have or whether you have a health condition.

How to Calculate Your BMI Without Doing the Math

Once you know your height and weight, manually calculating BMI isn’t difficult, but there is no reason to repeat the formula every time you want to check it.

Our BMI Calculator lets you enter your measurements and calculates the result for you.

It’s particularly useful when:

• Your height is in feet and inches
• Your weight is in pounds
• You normally use kilograms and centimeters
• You want to check a calculation quickly
• You don’t want to work through the formula manually

If you do calculate your BMI by hand, the calculator can also be useful for checking your result.

Does BMI Work the Same for Men and Women?

The basic adult BMI formula is the same for men and women:

BMI = weight ÷ height²

There isn’t a separate adult formula where you multiply or divide the result simply because you are male or female.

However, BMI doesn’t account for individual differences in body composition. Two people with the same BMI can have different amounts of muscle and body fat.

For adults, the standard BMI categories are applied regardless of sex.

Does Age Affect BMI?

It depends on the person’s age.

For adults age 20 and older, the standard BMI categories are used regardless of age.

Children and teenagers are different because their bodies are still growing.

For people between 2 and 19 years old, BMI is calculated from height and weight but then interpreted using BMI-for-age percentiles, taking the child’s age and sex into account.

This means you should not take a child’s BMI and compare it with the adult 18.5, 25, and 30 cutoffs.

How to Calculate BMI for Children and Teenagers

The mathematical calculation is still:

BMI = Weight (kg) ÷ Height (m)²

But the result needs to be interpreted differently.

For children and teenagers ages 2 through 19, BMI is compared with other children of the same age and sex. The result is expressed as a BMI-for-age percentile.

The CDC uses these categories:

Because children grow at different rates, the percentile approach gives a more appropriate way to track BMI during childhood and adolescence.

What About BMI During Pregnancy?

Pregnancy is another situation where you should not simply take the standard adult BMI chart and apply it to current pregnancy weight.

During pregnancy, weight gain includes more than body fat. It can include the baby, placenta, amniotic fluid, increased blood volume, breast tissue, and other normal changes.

Pre-pregnancy BMI is commonly used when discussing recommended weight gain during pregnancy.

So if you’re pregnant and your goal is to understand how much weight you should gain during pregnancy, a BMI result isn’t the right tool for answering that question on its own.

Our Pregnancy Weight Gain Calculator is more appropriate for looking at pregnancy-specific weight gain guidance.

Why BMI Isn’t a Perfect Measure of Health

BMI is useful partly because it is simple. You only need height and weight, and the calculation takes seconds.

But that simplicity is also its biggest limitation.

BMI does not directly measure:

• Body fat percentage
• Muscle mass
• Bone mass
• Where body fat is stored
• Overall fitness
• Blood pressure
• Blood sugar
• Cholesterol
• Other individual health factors

The CDC describes BMI as a screening measure and recommends considering it alongside other factors such as health behaviors, medical history, physical examination findings, and laboratory findings.

For example, consider a muscular athlete

A person who has built a significant amount of muscle may weigh more than someone of the same height with less muscle.

Because BMI only sees height and total weight, the muscular person may have a BMI in the overweight or obesity category even though BMI doesn’t tell us how much of that weight comes from muscle.

That’s one reason BMI should not be treated as a direct measurement of body fat.

BMI and Body Fat Percentage Are Not the Same

It’s easy to confuse these two numbers, but they measure different things.

BMI uses:

• Height
• Weight

Body fat percentage attempts to estimate the proportion of your body weight that is fat.

Two people can have the same BMI and very different body compositions.

For example, a person who lifts weights regularly and has a high amount of muscle may have the same BMI as another person with much less muscle and a higher proportion of body fat.

BMI can still be useful as a screening measure, but it cannot replace a more detailed assessment of body composition when that information is needed.

BMI and Waist Size

BMI tells you about weight relative to height, but it doesn’t tell you where that weight is distributed.

Waist circumference can provide additional information about abdominal fat, which is one reason it is sometimes considered alongside BMI when assessing health risk.

You shouldn’t try to replace BMI with waist measurement, either. They answer different questions.

A more complete assessment can consider several pieces of information rather than relying on one number.

Can Athletes Have a High BMI?

Yes.

This is one of the clearest examples of why BMI needs context.

Suppose two people are the same height and weigh exactly the same amount. Their BMI will be identical, even if one has substantially more muscle and less body fat than the other.

BMI has no way to distinguish those differences because the formula uses only height and weight.

For people with unusually high muscle mass, BMI may therefore overstate the amount of body fat suggested by the category.

Is a Low BMI Always Unhealthy?

Not necessarily, but a low BMI should not be treated as a target.

For adults, a BMI below 18.5 falls into the underweight category.

BMI alone cannot explain why someone has a low weight.

A lower weight may be related to many different circumstances, including natural body build, changes in eating, illness, or unintentional weight loss.

If someone is experiencing significant or unexplained weight loss, difficulty eating, or concerns about their health, the BMI number should not be used as a diagnosis.

BMI and eating disorders

BMI also cannot diagnose anorexia nervosa or another eating disorder.

An eating disorder involves much more than a person’s BMI, and someone does not need to meet a particular BMI number to have an eating disorder.

If concerns about restrictive eating, fear of weight gain, or other eating-related behaviors are present, those concerns deserve attention independently of the BMI result.

Common BMI Calculation Mistakes

A correct formula can still produce the wrong answer if the measurements are handled incorrectly.

Using centimeters as meters

If your height is 175 cm, don’t enter 175 into the standard meter formula.

Convert it first:

175 cm = 1.75 m

Forgetting to square your height

BMI isn’t:

Weight ÷ Height

It’s:

Weight ÷ Height²

For a height of 1.75 m:

1.75² = 3.0625

Using feet instead of inches

The imperial formula expects height in inches.

For someone who is 5 feet 9 inches:

(5 × 12) + 9 = 69 inches

Mixing measurement systems

Don’t put kilograms into the pounds-and-inches formula or centimeters into the meter formula without making the required conversion.

Using adult BMI categories for children

Children and teenagers require BMI-for-age percentiles rather than the standard adult cutoffs.

Assuming BMI is a diagnosis

A BMI category is a screening result. It does not tell the entire story about a person’s health.

Why Does My BMI Calculator Give a Different Answer?

If two calculators produce slightly different results, check a few things before assuming one is wrong.

Height precision

Using 175 cm versus 175.5 cm can change the result.

Weight precision

A weight entered as 70 kg will produce a slightly different BMI from 70.5 kg.

Rounding

One calculator may round height or weight before calculating, while another may use the exact values entered.

Unit conversion

Converting between pounds/kilograms or feet/meters can introduce small differences depending on when rounding occurs.

For children and teenagers, differences can also occur because BMI-for-age calculations depend on precise age, height, weight, and the growth reference being used. The CDC notes that differences in rounding can produce slightly different results between programs.

For an adult, a difference of a few hundredths may simply come down to rounding rather than a fundamentally different formula.

Calculate Your BMI With CalculatorSee

If you already know your height and weight, you don’t need to work through the formula every time.

Use the BMI Calculator to enter your measurements and get your BMI without doing the calculations yourself.

You can also use the manual formula in this guide if you want to understand or double-check the result.

If you’re looking beyond BMI, CalculatorSee also has tools for estimating a healthy weight, checking an overweight range, and looking at pregnancy weight gain. Each tool is designed for a slightly different question, so the right calculator depends on what you’re trying to find out.

The Bottom Line

Calculating BMI is simple:

BMI = Weight ÷ Height²

With metric measurements, use kilograms and meters. With pounds and inches, use the imperial formula:

BMI = [Weight (lb) ÷ Height (in)²] × 703

For adults, the resulting number can be compared with standard BMI categories ranging from underweight to obesity. But BMI is a screening measure, not a complete measurement of your health. It does not directly measure body fat and can be less informative for people with unusually high muscle mass.

The calculation also changes in how it is interpreted for children and teenagers, and pregnancy requires a different approach to evaluating weight gain.

If you have your height and weight ready, you can use the CalculatorSee BMI Calculator to get your BMI instantly.