How to Calculate BMI: Formula, Chart, Categories & What Your BMI Means

Body Mass Index (BMI) is calculated by dividing your weight in kilograms by your height in meters squared. For example, an adult weighing 70 kg who measures 1.75 m tall has a BMI of approximately 22.9, which places them in the standard healthy weight category.

Public health organizations, including the Centers for Disease Control and Prevention (CDC) and the World Health Organization (WHO), use BMI as an accessible screening tool to track weight patterns across populations. It helps clinicians quickly assess whether an individual's weight may carry elevated risks for conditions such as high blood pressure, type 2 diabetes, or cardiovascular disease.

BMI serves as a screening benchmark rather than a medical diagnosis. It does not measure body fat directly, nor does it identify where fat is stored or differentiate dense muscle mass from adipose tissue. Below, you can test your numbers immediately using our live BMI calculator, review metric and imperial formulas, check adult BMI tables, and review what your score indicates.

What Is BMI?

Body Mass Index evaluates your body mass relative to your stature. Because people vary in height, looking at scale weight alone tells you very little about whether someone carries excess mass. A weight of 75 kg represents a healthy body mass for someone standing 185 cm tall, but that same weight represents significant excess mass for someone measuring 150 cm. BMI normalizes this relationship into a single index.

What does BMI stand for?

BMI stands for Body Mass Index. Belgian astronomer and statistician Adolphe Quetelet introduced the underlying mathematical concept during the 1830s while studying human growth curves and social statistics. For more than a century, researchers referred to it as the Quetelet Index. In 1972, physiologist Ancel Keys published landmark research in the Journal of Chronic Diseases proving that the ratio of weight divided by height squared correlated better with body fat percentage than other simple height-weight formulas. Keys gave the formula its modern name: Body Mass Index.

What does BMI measure?

BMI measures total body mass per unit of surface height. It does not measure body fat directly, nor does it measure visceral fat, subcutaneous fat, bone mineral density, or muscle mass. Instead, it acts as an indirect surrogate marker for body adiposity across wide populations.

Why is BMI used?

Medical professionals and public health agencies rely on BMI because it is non-invasive, inexpensive, and fast. Calculating BMI requires only two baseline measurements: body weight from a calibrated scale and height from a wall-mounted stadiometer or measuring tape. It provides an immediate baseline during routine clinical exams and epidemiological surveys without requiring expensive imaging equipment like DEXA scans or hydrostatic weighing tanks.

Is BMI a diagnosis?

No. BMI is strictly a screening test, not a diagnostic tool. The CDC explicitly advises that a high or low BMI indicates the need for further clinical evaluation rather than serving as a diagnosis of poor health or disease. A physician interprets a patient's BMI alongside their medical history, family risk factors, blood pressure, blood glucose, cholesterol levels, physical fitness, and diet.

How to Calculate BMI

Calculating BMI requires squaring your height and dividing your weight by that number. Depending on your preferred measurement system, you can use the metric formula or the imperial formula.

BMI formula in metric units

The international metric formula divides your weight in kilograms by your height in meters squared:

BMI formula in imperial units

If your weight is recorded in pounds and your height in inches, you divide weight by height in inches squared, then multiply by a conversion multiplier of 703:

Note on the 703 multiplier: One pound equals 0.453592 kg, and one inch equals 0.0254 meters. Converting pounds per square inch to kilograms per square meter yields (0.453592 ÷ 0.0254²) ≈ 703.07. Multiplying by 703 matches the imperial calculation directly to the international metric scale.

How to calculate BMI using kg and cm

Most people know their height in centimeters rather than meters. Here is the step-by-step arithmetic:

1. Convert centimeters to meters: Divide your height by 100. For example, 175 cm becomes 1.75 m.
2. Square your height in meters: Multiply the meter value by itself. For 1.75 m: 1.75 × 1.75 = 3.0625 m².
3. Divide weight by squared height: If you weigh 70 kg, divide 70 by 3.0625.
4. Calculate the final value: 70 ÷ 3.0625 = 22.857. Rounded to one decimal place, your BMI is 22.9.

How to calculate BMI using pounds and feet/inches

If you track weight in pounds and height in feet and inches, follow this method:

1. Convert your total height to inches: Multiply feet by 12 and add the remaining inches. For example, 5 feet 9 inches becomes (5 × 12) + 9 = 69 inches.
2. Square your height in inches: 69 × 69 = 4,761 in².
3. Divide weight in pounds by squared inches: If you weigh 160 lbs: 160 ÷ 4,761 ≈ 0.033606.
4. Multiply by 703: 0.033606 × 703 = 23.625. Rounded to one decimal place, your BMI is 23.6.

BMI Calculator vs. Manual Calculation

Working through the formulas by hand is straightforward, but people frequently run into common arithmetic mistakes:

• Forgetting to divide height in centimeters by 100 before squaring, leading to an impossibly tiny fraction.
• Squaring the weight instead of squaring the height.
• Converting feet to inches incorrectly (for example, assuming 5'8" is 58 inches rather than 68 inches).
• Leaving out the 703 conversion multiplier when using pounds and inches.

An automated tool eliminates manual conversion errors, lets you switch between metric and imperial systems instantly, and computes your personalized healthy weight target based on your height.

Adult BMI Categories

For men and women aged 20 and older, standard adult BMI categories set by the CDC and WHO group scores into four general categories:

BMI obesity classes

The obesity category is further divided into three clinical tiers to help healthcare professionals evaluate statistical health risks and determine appropriate care pathways:

BMI Chart by Height and Weight

This reference chart presents exact weight thresholds across common adult heights. For every height listed, we have calculated the underweight cutoff (BMI < 18.5), the healthy weight boundaries (BMI 18.5 to 24.9), the overweight threshold (BMI ≥ 25.0), and the obesity line (BMI ≥ 30.0).

How to read and use the chart

Find your height along the left column. Trace directly right to locate your healthy weight window. Notice that for every height, there is a roughly 15 to 23 kg span where weight remains classified as healthy. This wide window accounts for normal variations in skeletal frame size, natural bone density, and everyday hydration fluctuations.

What Does My BMI Mean?

Your BMI score places your current height-to-weight proportion into an epidemiological category. Here is how each category should be interpreted objectively:

BMI below 18.5 (Underweight)

A score under 18.5 indicates that your body mass is below expected thresholds for your height. This category screens for insufficient caloric or protein intake, reduced bone mineral density, anemia, weakened immune resistance, or potential hormonal disruptions. If your score sits here without intentional athletic training or a naturally lean constitution, consult a physician or registered dietitian to evaluate your nutrient absorption, thyroid function, and overall metabolic health.

BMI from 18.5 to 24.9 (Healthy weight)

A score in this range indicates that your weight sits in the standard statistical window associated with lower long-term risk of weight-related chronic conditions. However, a healthy BMI does not guarantee perfect health. People who lead sedentary lifestyles or carry elevated visceral abdominal fat can still develop metabolic issues like insulin resistance or dyslipidemia, a condition sometimes called normal-weight metabolic obesity.

BMI from 25.0 to 29.9 (Overweight)

A score between 25.0 and 29.9 indicates excess body weight relative to stature. Across general populations, this range correlates with higher rates of hypertension and elevated blood triglycerides. However, because BMI cannot measure body fat directly, highly active individuals and strength athletes frequently fall into this bracket due to dense skeletal muscle. Rather than assuming excess adiposity, use a tape measure to check your waist circumference.

BMI of 30.0 or higher (Obesity)

A BMI of 30.0 or above indicates significant excess body mass relative to height. In clinical studies, this range correlates with higher risks of coronary artery disease, osteoarthritis, obstructive sleep apnea, non-alcoholic fatty liver disease, and type 2 diabetes. Healthcare providers use this category as a starting point to tailor nutrition plans, exercise guidance, and metabolic monitoring.

Is BMI Different for Women and Men?

The mathematical formula and standard adult category cutoffs are identical for men and women according to CDC and WHO standards. An adult woman measuring 165 cm and weighing 65 kg has a BMI of 23.9, and an adult man of the same height and weight has the exact same BMI of 23.9.

However, underlying body composition differs markedly between the sexes:

• Essential fat requirements: Women biologically require approximately 10% to 13% essential body fat to support reproductive endocrinology, breast tissue, and regular menstrual cycles. Men require only 2% to 5% essential fat.
• Average body fat percentage: At the identical BMI of 23, an average adult woman typically carries 25% to 30% body fat, whereas an average adult man carries roughly 15% to 20% body fat.
• Fat storage patterns: Women tend to store fat subcutaneously in the hips, buttocks, and thighs (gynoid distribution). Men tend to accumulate fat deeper in the abdominal cavity around internal organs (android distribution, or visceral fat). Visceral fat produces higher systemic inflammation than subcutaneous fat.

Does BMI Change With Age?

Age affects how BMI should be interpreted, even though standard adult thresholds apply to all individuals aged 20 and older.

BMI for adults (Ages 20 to 64)

For young and middle-aged adults, the standard 18.5 to 24.9 healthy range serves as the official public health baseline. During these decades, tracking weight stability and waist circumference helps identify early metabolic shifts.

BMI for older adults (Ages 65 and older)

As humans age past 65, skeletal muscle mass naturally declines (a process called sarcopenia) while body fat percentage frequently increases, even if total scale weight stays constant.

Epidemiological studies in geriatric medicine have identified what researchers describe as the "obesity paradox" in older adults: having a slightly higher BMI (roughly 23 to 28) often correlates with lower mortality rates, reduced risk of bone fractures during accidental falls, and better resilience when recovering from acute illnesses or surgery. For older adults, unintentional weight loss is often a much more serious clinical concern than carrying modest extra weight.

BMI for children and teenagers

Standard adult categories cannot be applied to children or teenagers aged 2 to 19 because their bodies are growing rapidly and body composition shifts dramatically across puberty.

Is BMI Calculated Differently for Children?

The arithmetic calculation for children is identical: weight in kilograms divided by height in meters squared. However, how the result is interpreted is completely different.

In pediatric healthcare, a child's raw BMI is plotted on standardized CDC or WHO growth charts to determine their BMI-for-age percentile, which compares the child to thousands of other boys or girls of the exact same age:

BMI Cutoffs for Asian & Indian Adults

One common point of confusion is whether the WHO changed official BMI cutoffs for Asian and Indian populations.

In 2004, the WHO convened an Expert Consultation published in The Lancet to examine evidence showing that Asian populations develop increased risks of type 2 diabetes and cardiovascular disease at substantially lower BMI levels than European populations. The consultation concluded that the international classification (18.5–24.9 healthy, 25+ overweight, 30+ obesity) should remain the official global standard to preserve worldwide epidemiological consistency.

However, the WHO recommended that governments and public health organizations identify additional public health action points for Asian populations:

• 23.0 to 27.4 kg/m²: Increased risk (action point for lifestyle and dietary guidance).
• 27.5 kg/m² or higher: High risk (action point for clinical screening of metabolic markers).

Consensus guidelines for Asian Indians (ICMR / MoHFW)

In India, the Ministry of Health and Family Welfare (MoHFW) alongside the Indian Council of Medical Research (ICMR) and National Diabetes, Obesity, and Cholesterol Foundation (N-DOC) established tailored clinical criteria for Asian Indians:

This explains why an Indian adult with a BMI of 24.2 might be advised by their doctor to manage their weight, even though an international chart categorizes 24.2 as "normal."

Limitations of BMI

BMI remains widely used because of its simplicity, but understanding its limitations ensures you do not draw inaccurate conclusions about your personal physical condition.

1. BMI does not measure body fat directly

Two individuals can have the exact same height (178 cm), the exact same weight (80 kg), and the exact same BMI (25.2). Yet one may be an active distance runner with 14% body fat, while the other is completely sedentary with 28% body fat. BMI treats all body mass identically.

2. BMI does not distinguish muscle from fat

Skeletal muscle tissue is approximately 18% denser by volume than adipose fat tissue. Athletes, weightlifters, gymnasts, and physical laborers carry elevated muscle mass that drives their scale weight up. Under standard BMI calculators, these individuals are routinely classified as overweight or even obese despite having lean builds and outstanding cardiovascular fitness.

3. BMI doesn't show where fat is stored

Fat distribution plays a major role in cardiometabolic risk. Visceral fat accumulates deep in the abdominal cavity around vital organs, secreting inflammatory cytokines that drive insulin resistance and plaque buildup in arteries. In contrast, subcutaneous fat stored just below the skin on the legs or hips poses much lower metabolic risk. BMI cannot detect whether your mass is stored around your waist or on your limbs.

4. BMI may not tell the whole story for older adults

When older adults lose muscle due to inactivity or aging, their total weight can drop while their relative body fat percentage rises. An older person might maintain a "healthy" BMI of 22 while silently developing sarcopenic obesity, characterized by weak muscles, poor balance, and high relative adiposity.

5. BMI has limitations during pregnancy

During pregnancy, rapid weight gain reflects the developing fetus, amniotic fluid, placenta, expanded maternal blood volume, and breast tissue. Applying standard BMI equations during pregnancy produces clinically inaccurate results. Obstetricians use pre-pregnancy BMI strictly to advise on safe gestational weight gain targets.

What Should You Consider Alongside BMI?

To get a clear, balanced picture of your personal health, pair your BMI result with other simple, evidence-based metrics:

• Waist Circumference: Measure your waist directly above your hip bones with a flexible tape measure after exhaling. The National Institutes of Health (NIH) notes that health risks rise sharply at a waist circumference over 102 cm (40 inches) for men and over 88 cm (35 inches) for women (for Asian adults: over 90 cm for men and over 80 cm for women).
• Waist-to-Height Ratio (WHtR): A straightforward clinical rule of thumb: keep your waist circumference to less than half your height (WHtR < 0.5). If you stand 180 cm tall, your waist should ideally measure under 90 cm.
• Cardiovascular Fitness: Resting heart rate, heart rate recovery after exercise, and aerobic endurance provide direct feedback on heart and lung health.
• Metabolic Blood Panels: Routine blood testing for fasting blood glucose, HbA1c, lipid profile (HDL, LDL, triglycerides), and liver enzymes evaluates what is happening inside your blood vessels regardless of scale weight.
• Blood Pressure: Maintaining resting blood pressure below 120/80 mmHg is one of the strongest protective factors against cardiovascular events.

BMI Calculation Examples

Review these four worked examples to see how the formulas work in practical situations:

Frequently Asked Questions About BMI

Key Takeaways