Free BMI Calculator

What Is BMI?

Body mass index, usually shortened to BMI, is a calculation that compares a person's weight with the square of their height. It produces a single number that is commonly used as a screening measure for weight status. The basic idea is simple: weight relative to height. A person who is taller can generally weigh more than a shorter person before reaching the same BMI, because height is squared in the formula.

For adults age 20 and older, the resulting BMI can be compared with standard adult BMI categories. For children and teens ages 2 through 19, the raw BMI number is calculated in the same basic way, but it must be interpreted differently, because children are still growing. BMI for a child or teen is evaluated using age- and sex-specific BMI-for-age percentiles rather than fixed adult cutoffs.

BMI can be useful because it is quick, inexpensive, easy to calculate, widely recognized, and useful for population screening. But BMI is not a diagnosis and it does not directly measure body fat. CDC guidance on BMI as a screening measure explains that BMI should be considered along with other health information rather than treated as a complete assessment by itself.

How Do You Calculate BMI?

BMI uses height and weight. For metric units, BMI equals weight in kilograms divided by height in meters squared. For U.S. customary units, BMI equals 703 times weight in pounds divided by height in inches squared.

Suppose an adult weighs 160 pounds and is 5 feet 8 inches tall. First convert the height to total inches: 5 × 12 = 60, and 60 + 8 = 68 inches. Now square the height: 68 × 68 = 4,624. Multiply the weight by 703: 160 × 703 = 112,480. Divide: 112,480 ÷ 4,624 ≈ 24.33. The person's BMI is approximately 24.3. Using the standard adult categories, that falls within the Healthy Weight BMI category.

If you prefer to watch the calculation worked visually, Dr SMART team also demonstrates a simple BMI calculation method in Calculate Your BMI using this simple method.

What Are the Adult BMI Categories?

For adults age 20 and older, BMI categories are based on the BMI number itself. The adult categories used on this page follow CDC adult BMI categories. The categories are: Underweight, BMI below 18.5; Healthy Weight, BMI 18.5 to less than 25; Overweight, BMI 25 to less than 30; and Obesity, BMI 30 or greater. The obesity category is further divided into Class 1, BMI 30 to less than 35; Class 2, BMI 35 to less than 40; and Class 3, sometimes called severe obesity, BMI 40 or greater.

These categories are screening categories. They do not mean that every person with the same BMI has the same body composition, health status, fitness level, or health risks.

Is BMI Different for Women and Men?

For adults age 20 and older, the standard BMI calculation and adult BMI category thresholds do not change because someone is a woman or a man. The BMI formula is still based on height and weight. This is important because searches such as "BMI women," "women BMI," "BMI calculator women," and "BMI calculator for women" can make it sound as though women use an entirely different adult BMI chart. They do not. An adult woman with a BMI of 24 and an adult man with a BMI of 24 both fall within the same adult BMI category.

That does not mean the two people necessarily have the same body-fat percentage, muscle mass, fat distribution, fitness, or health history. BMI does not measure those things directly. This is one reason BMI should be considered a screening tool rather than a complete description of a person's health. If you want an estimate focused more directly on body fat, use the CalculateThisWay Body Fat Calculator.

What Does BMI 27 Mean?

A BMI of 27 falls within the adult Overweight BMI category because it is between 25 and less than 30. That describes the BMI category only. It does not tell you your exact body-fat percentage, where body fat is stored, how much muscle you have, your blood pressure, your cholesterol, your blood sugar, your fitness level, or your complete health status.

Someone searching "BMI 27" should be able to get a direct answer without reading the entire page first. Answer: for an adult age 20 or older, a BMI of 27 falls within the Overweight BMI category. BMI is a screening measure, not a diagnosis.

What Is a Healthy BMI for Adults?

The standard adult Healthy Weight BMI category runs from 18.5 to less than 25. It is commonly displayed as 18.5 to 24.9. The same adult range applies to adult women and men. This does not mean that 24.9 is a perfect target, or that 25.0 suddenly defines someone's health. BMI categories are screening ranges. They are useful for organizing measurements, but a person's health is more complex than a cutoff to one decimal place.

What Is a Healthy Weight for My Height?

Because BMI depends on both height and weight, the adult Healthy Weight BMI range can be converted into an estimated weight range for a specific height. That is why the separate Healthy Weight Calculator can be consolidated into this BMI Calculator. For an adult, CalculateThisWay can calculate the weights that correspond to the lower and upper ends of the standard Healthy Weight BMI range for the user's height. For example, two adults can both be within the same BMI category while having very different weights, because one person is much taller than the other.

The result is displayed as a healthy adult BMI range of 18.5 to 24.9 and a healthy weight range for your height, calculated from your entered height. This is a BMI-based screening range. It is not an individualized prescription for what someone must weigh.

What Is an Ideal Weight?

The phrase "ideal weight" sounds more precise than it really is. There is no single universally correct body weight for every person of the same height. Different historical height-based formulas can produce different estimates. That is why the retired Ideal Weight Calculator is integrated here as Height-Based Reference Weight Estimates rather than presented as a medically perfect body weight. The old CalculateThisWay Ideal Weight Calculator used four established formulas, and this BMI page preserves those calculations in the optional section above.

The result clearly distinguishes between the BMI-based healthy weight range and historical formula-based reference weight estimates. They answer different questions. The BMI range asks: what range of weights corresponds to the standard adult Healthy Weight BMI category for this height? Reference formulas ask something more like: what body weight does this particular height-based formula estimate? Neither one can determine a perfect weight for an individual.

BMI Healthy Weight Range vs. Ideal Weight Estimate

These two concepts should not be presented as the same thing. The BMI healthy weight range uses height and the BMI boundaries 18.5 and 24.9 to produce a range. The height-based reference weight estimate uses a historical formula, height, and sometimes sex, to produce one estimated value per formula. One is a BMI screening range. The other is a formula estimate. This calculator shows both clearly when you choose to open the optional Height-Based Reference Weight Estimates section.

How Is BMI Calculated for Children and Teens?

BMI itself is still calculated from height and weight. But children and teens should not be interpreted using adult BMI cutoffs. For ages 2 through 19, BMI is evaluated using BMI-for-age percentile, which considers age and sex. CDC's CDC Child and Teen BMI Calculator reports BMI, BMI percentile, and BMI category. Why is this different? Children are still growing. Normal changes in body size and body composition occur throughout childhood and adolescence. A BMI number that means one thing for an adult may not have the same interpretation for a growing child.

What Are the BMI Categories for Children and Teens?

When an accurate CDC percentile calculation is available, child and teen categories are based on BMI-for-age percentile: Underweight is less than the 5th percentile; Healthy Weight is 5th percentile to less than the 85th percentile; Overweight is 85th percentile to less than the 95th percentile; and Obesity is 95th percentile or greater. CDC also defines severe obesity using an expanded threshold based on the percentage of the 95th percentile and/or BMI. The important point for a parent or caregiver is this: do not take a child's raw BMI and compare it directly with the adult 18.5, 25, and 30 cutoffs. Age and sex are necessary for interpretation.

What Is a BMI Percentile?

A percentile describes where a child's BMI falls relative to the BMI distribution for children of the same age and sex in the reference population. For example, a BMI percentile of 75 does not mean "75% body fat." It means the child's BMI is at a certain relative position compared with children of the same age and sex in the reference data. This distinction should be prominently explained, because BMI and BMI percentile are not the same measurement.

Is BMI Accurate for Children?

BMI can be useful as a screening measure for children and teens, but the interpretation should consider growth and development. A child's BMI percentile can be one piece of information used with growth history, health history, physical development, and other clinical information. This calculator does not diagnose a child. If there are concerns about a child's growth or weight, discuss them with a qualified health professional.

What Can BMI Tell You?

BMI can help describe weight relative to height and, for adults, place that measurement into a standard screening category. It can also be useful for population research, tracking patterns over time, and initial screening. But BMI does not directly measure body fat, muscle, bone density, fat distribution, fitness, or metabolic health. That means two people with the same BMI can have very different bodies.

What Are the Limitations of BMI?

One important limitation is that BMI does not separate fat mass from lean mass. A muscular person can have a higher BMI partly because muscle contributes to total body weight. BMI also does not show where fat is distributed. It does not account directly for body composition, physical fitness, blood pressure, blood glucose, cholesterol, sleep, nutrition quality, or medical history. CDC describes BMI as one potential health indicator that should be considered with other information. If you want an estimate aimed more directly at body fat, use CalculateThisWay's Body Fat Calculator.

BMI vs. Body Fat Percentage

BMI and body-fat percentage are not interchangeable. BMI uses height and weight. Body-fat percentage estimates how much of total body weight is fat mass. A person can have a relatively high BMI and a comparatively low body-fat percentage if they carry substantial muscle mass. Conversely, a person can fall within a standard BMI category while still having other health factors that deserve attention. Use the Body Fat Calculator for body-fat estimation.

BMI vs. BMR

BMI and BMR sound similar but answer completely different questions. BMI compares weight with height. BMR estimates the energy your body uses at rest. If you want to estimate resting calorie needs rather than weight status, use the existing BMR Calculator.

BMI vs. Calorie Needs

BMI does not tell someone how many calories they need to eat each day. Daily calorie needs depend on factors such as body size, age, activity, and energy expenditure. Use the CalculateThisWay Calorie Calculator for that estimate. This BMI page stays focused on weight relative to height rather than turning into a calorie calculator.

Does Age Affect Adult BMI Categories?

For adults age 20 and older, the standard adult BMI categories do not change because someone is 25, 45, or 65. Age may matter to overall health and body composition, but it is not part of the standard adult BMI category calculation. For children and teens, however, age is essential, because interpretation uses BMI-for-age percentiles. This is why the calculator above asks "Who Is This BMI For?" before deciding how to interpret the result.

Does Sex Affect Adult BMI Categories?

For adults, no. The standard BMI calculation and adult category thresholds are the same regardless of sex. Sex becomes relevant on this page only for child/teen BMI percentile interpretation and, optionally, for the historical height-based reference weight formulas. This page does not imply that women have a different adult BMI category chart than men.

BMI for Women

People frequently search "BMI women," "women BMI," "BMI calculator for women," and "what's my BMI woman." For an adult woman, BMI is calculated from her height and weight using the same adult formula used for an adult man. Example: a woman who is 5 ft 4 in tall (64 inches) and weighs 140 lb has a BMI of 703 × 140 ÷ 64² ≈ 24.0, which falls within the Healthy Weight category. The adult category does not change because the user is female.

BMI for Men

For an adult man, the calculation is also weight relative to height. Example: a man who is 6 ft 0 in tall (72 inches) and weighs 190 lb has a BMI of 703 × 190 ÷ 72² ≈ 25.8, which falls within the Overweight category. Again, adult category cutoffs are not sex-specific.

Can BMI Be Too Low?

An adult BMI below 18.5 falls within the Underweight BMI category. A low BMI can have many possible explanations. This calculator does not diagnose the reason, and it does not make assumptions about nutrition, illness, eating disorders, or medical conditions. It simply explains the category and the limitation of BMI as a screening measure.

What Does Overweight Mean on a BMI Chart?

For adults, BMI 25 to less than 30 is categorized as Overweight. This is a BMI screening classification. It is not a complete judgment of a person's health.

What Does Obesity Mean on a BMI Chart?

For adults, BMI 30 or greater is in the obesity category, subdivided into Class 1, Class 2, and Class 3. This page uses person-first phrasing, such as "BMI falls within the Class 1 obesity category," rather than "You are obese."

How Does Height Affect BMI?

Height has a large effect on BMI because height is squared in the denominator. That is why simply comparing two people's weights without considering height can be misleading. A 180-pound person who is 5 ft 4 in and a 180-pound person who is 6 ft 2 in will not have the same BMI.

How Does Weight Affect BMI?

When height stays the same, higher weight produces higher BMI. When weight stays the same, greater height produces lower BMI. This does not mean gaining or losing a specific amount of weight automatically improves health. It only describes the mathematical relationship in the BMI formula.

How Can I Calculate BMI Manually?

U.S. example: weight 180 lb, height 5 ft 10 in. Convert height: 5 × 12 + 10 = 70 inches. Square: 70² = 4,900. Multiply: 180 × 703 = 126,540. Divide: 126,540 ÷ 4,900 ≈ 25.82. BMI: 25.8.

Metric example: weight 75 kg, height 1.75 m. Square height: 1.75² = 3.0625. BMI: 75 ÷ 3.0625 ≈ 24.49. BMI: 24.5.

Why Does the Calculator Show a Healthy Weight Range?

The separate Healthy Weight Calculator is retired because its core calculation belongs naturally with BMI. Once your height is known, the calculator can reverse the adult BMI formula to estimate the weight range corresponding to BMI 18.5 through BMI 24.9. This makes the result more useful than simply returning "Your BMI is 24.3." The page instead helps you see your current BMI, your BMI category, the standard adult Healthy Weight BMI range, and the estimated BMI-based healthy weight range for your entered height, all without requiring a separate overlapping calculator.

Why Does the Page Also Offer Reference Weight Estimates?

The retired Ideal Weight Calculator served a different but related search intent. Rather than maintaining a separate overlapping page, this BMI calculator includes those established height-based estimates as an optional secondary feature, clearly labeled Reference Weight Estimates, not "Your Perfect Weight." Different formulas may produce different answers. That difference itself teaches something important: there is no universal formula that can identify one exact ideal body weight for every individual.

Should I Use BMI or Body Fat Percentage?

Use BMI when you want a quick height-and-weight screening calculation. Use body-fat percentage when you want an estimate focused specifically on fat mass relative to total body weight. Neither number by itself gives a complete picture of health. See the Body Fat Calculator.

Should I Use BMI or the Calorie Calculator?

Use BMI for weight relative to height. Use the Calorie Calculator for estimated daily calorie needs.

Should I Use BMI or BMR?

Use BMI for weight category screening. Use the BMR Calculator for estimated calories used at rest.

Common BMI Mistakes

Using Adult Categories for Children

Children and teens require BMI-for-age percentile interpretation.

Thinking BMI Directly Measures Body Fat

BMI uses height and weight. It does not directly measure body-fat percentage.

Thinking Women Need a Different Adult BMI Chart

Adult BMI categories are not different for women and men.

Treating BMI as a Diagnosis

BMI is a screening measure.

Thinking 24.9 Is Automatically Healthy and 25.0 Is Automatically Unhealthy

Category cutoffs organize measurements but do not capture every aspect of individual health.

Calling a Formula Estimate a Perfect Weight

Height-based reference formulas are estimates, not prescriptions.

Entering Height Incorrectly

For U.S. units, 5 ft 8 in must be converted to 68 inches, not 5.8 feet.

Mixing Metric Units

If using the standard metric formula, height should be in meters, not centimeters.

What Should You Leave This Page Knowing?

Do not leave knowing only "My BMI is 24.3." Leave knowing:

• I understand what BMI stands for.
• I know how BMI is calculated.
• I know how pounds and inches are used in the U.S. formula.
• I know how kilograms and meters are used in the metric formula.
• I understand the adult BMI categories.
• I know that adult BMI categories do not change because someone is a woman or a man.
• I understand what BMI 27 means for an adult.
• I know the standard adult Healthy Weight BMI range.
• I know how my height can be used to estimate the adult BMI-based Healthy Weight range.
• I understand the difference between a BMI healthy-weight range and a historical reference-weight formula.
• I know there is no single universal perfect body weight.
• I know child and teen BMI is interpreted differently from adult BMI.
• I know that children and teens use BMI-for-age percentiles.
• I know age and sex matter for child and teen percentile interpretation.
• I know not to apply adult categories to children.
• I understand that BMI does not directly measure body fat.
• I understand that BMI does not distinguish muscle from fat.
• I know BMI is a screening measure rather than a diagnosis.
• I know when the Body Fat Calculator may be more relevant.
• I know when the BMR Calculator may be more relevant.
• I know when the Calorie Calculator may be more relevant.

And most importantly: I understand what my BMI number does and does not tell me. That is what the CalculateThisWay BMI Calculator should accomplish.