BMI Calculator is a free online tool that helps you calculate your Body Mass Index based on your height and weight. It quickly shows whether you are underweight, normal, overweight, or obese.

BMI Calculator

Calculate your Body Mass Index and find your healthy weight range

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Body Mass Index

Underweight Normal Overweight Obese

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Detailed Breakdown

Health Tip

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BMI Categories (CDC / WHO)

About This BMI Calculator

Body Mass Index (BMI) is a simple measure that uses your height and weight to estimate whether your weight is in a healthy range. This calculator defaults to U.S. standard units (feet, inches, and pounds) and gives you a complete breakdown including your healthy weight range, BMI category, and a visual scale showing exactly where you stand — consistent with guidelines from the CDC and WHO.

Defaults to U.S. Imperial units (ft / in / lb) — switch to metric anytime.
Get your healthy weight range based on your exact height, plus how much you'd need to gain or lose to reach it.
Visual BMI scale shows exactly where your result falls — underweight, normal, overweight, or obese.
Full CDC/WHO BMI category table for quick reference and comparison.
Personalized health tips based on your result.

Disclaimer: BMI is a general screening tool and does not directly measure body fat or account for muscle mass, bone density, age, or sex distribution of fat. It is not a diagnostic tool. For a complete health assessment, please consult a qualified U.S.-licensed healthcare professional.

What Is BMI and What Does It Tell You?

Quick Answer

Body Mass Index (BMI) is a number calculated from a person's weight and height. It is used as a simple screening tool to categorize a person as underweight, normal weight, overweight, or obese — helping identify potential weight-related health risks. The CDC and WHO both recommend BMI as a low-cost population-level screening measure.

BMI was originally developed in the 1830s by Belgian mathematician Adolphe Quetelet as a way to study the average build of populations, not individuals. It later became known as the "Quetelet Index" before being renamed "Body Mass Index" in the 1970s by physiologist Ancel Keys, who studied its usefulness for assessing weight-related health risk across large groups of people.

Today, BMI is used widely in the United States by health organizations including the Centers for Disease Control and Prevention (CDC) and the World Health Organization (WHO) as a quick, low-cost screening method. It does not diagnose body fatness or health directly, but a high or low BMI can be a signal to look more closely at other health indicators.

BMI Formula: How Is It Calculated?

The BMI formula is the same for adults of any gender, and only requires two measurements: height and weight. There are two versions of the formula depending on which unit system you use.

Imperial Formula (U.S. Standard)

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

Metric Formula

BMI = weight (kg) ÷ height (m)²

Worked Example (Imperial — U.S. Standard)

Suppose a person weighs 154 lb and is 5 ft 9 in (69 inches) tall. Their BMI is: (154 ÷ 69²) × 703 = (154 ÷ 4,761) × 703 = 22.7. A BMI of 22.7 falls within the normal weight range (18.5–24.9).

Worked Example (Metric)

Suppose a person weighs 70 kg and is 1.75 m tall. Their BMI is: 70 ÷ (1.75 × 1.75) = 70 ÷ 3.0625 = 22.9, which also falls within the normal range.

BMI Categories Explained (CDC / WHO Classification)

The CDC and WHO define the following standard BMI categories for adults aged 18 and over. These ranges apply to both men and women, though individual health risk can vary based on factors such as age, muscle mass, and ethnicity.

BMI Range	Category	General Health Risk
Below 16.0	Severe Thinness	High risk of nutritional deficiency, weakened immunity
16.0 – 16.9	Moderate Thinness	Elevated risk of health problems
17.0 – 18.4	Mild Thinness	Slightly elevated risk
18.5 – 24.9	Normal Weight	Lowest risk for most people
25.0 – 29.9	Overweight	Moderately increased risk
30.0 – 34.9	Obese Class I	High risk
35.0 – 39.9	Obese Class II	Very high risk
40.0 and above	Obese Class III (Severe Obesity)	Extremely high risk

How to Use This BMI Calculator

Choose your unit system — the calculator defaults to U.S. Imperial (feet, inches, and pounds). Switch to metric if preferred.
Select your biological sex — used for the ideal weight estimate, which differs slightly between males and females.
Enter your age — used for context in the breakdown, as BMI interpretation can vary slightly by life stage.
Enter your height and weight — type the values into the input fields.
Tap "Calculate BMI" — instantly see your BMI score, category, healthy weight range, and a full detailed breakdown including BMI Prime, Ponderal Index, Body Surface Area, and an estimated ideal weight.

Healthy Weight Range by Height (U.S. Reference)

Because BMI depends on height, the actual weight range considered "normal" (BMI 18.5–24.9) is different for everyone. The table below shows approximate healthy weight ranges for common heights, as used in U.S. clinical settings.

Height	Healthy Weight Range (lb)	Healthy Weight Range (kg)
5'0" (152 cm)	94 – 127 lb	42.7 – 57.6 kg
5'4" (163 cm)	108 – 146 lb	49.2 – 66.4 kg
5'6" (168 cm)	115 – 155 lb	52.1 – 70.3 kg
5'8" (173 cm)	122 – 165 lb	55.4 – 74.7 kg
5'10" (178 cm)	129 – 174 lb	58.6 – 79.0 kg
6'0" (183 cm)	137 – 184 lb	62.0 – 83.6 kg
6'2" (188 cm)	144 – 195 lb	65.4 – 88.3 kg

Limitations of BMI: Why It Isn't the Whole Picture

While BMI is widely used in U.S. healthcare because it's quick, free, and requires no special equipment, it has several well-documented limitations:

Doesn't distinguish muscle from fat: A muscular athlete and a sedentary person of the same height and weight will have identical BMI scores, even though their body composition and health risks may be very different.
Doesn't account for fat distribution: Abdominal (visceral) fat is associated with higher health risks than fat stored elsewhere, but BMI cannot detect this. Waist circumference measurements are often used alongside BMI in U.S. clinical assessments.
Less reliable across age groups: Older adults naturally carry more body fat for the same BMI due to age-related muscle loss (sarcopenia).
Ethnic variation: Research — including studies referenced by the CDC — suggests certain populations may face elevated health risks at lower BMI thresholds than standard WHO cutoffs, prompting some U.S. clinicians to use adjusted ranges.
Not designed for children, pregnant women, or very elderly individuals: These groups require different assessment methods. For children and teens, the CDC recommends age- and sex-specific BMI percentile charts.

Beyond BMI: Other Useful Metrics in This Calculator

BMI Prime

BMI Prime is your BMI divided by 25 (the upper limit of the normal range). A BMI Prime of 1.0 means you are right at the top of the normal weight boundary. Values below 1.0 indicate normal or underweight; values above 1.0 indicate overweight or obesity — making it easy to see proportionally how far you are from the healthy range.

Ponderal Index

The Ponderal Index uses the cube of height instead of the square, which some researchers consider more accurate for very tall or short individuals, since it scales more proportionally with body volume.

Body Surface Area (BSA)

BSA, calculated using the Mosteller formula, estimates the total surface area of your body in square meters. It is commonly used in U.S. medicine to calculate medication dosages, chemotherapy dosing, and fluid requirements.

Ideal Weight Estimate

This calculator uses the Devine formula (1974), still widely referenced in U.S. clinical settings — particularly for medication dosing — to estimate ideal body weight based on height and biological sex. It should be treated as a general reference, not a personal target.

How to Achieve or Maintain a Healthy BMI

Whether your BMI is below, within, or above the normal range, sustainable lifestyle habits tend to produce the best long-term results. The following align with recommendations from the CDC, the American Heart Association (AHA), and the Dietary Guidelines for Americans:

Follow a balanced diet: Prioritize vegetables, fruits, whole grains, lean proteins, and healthy fats. The USDA's MyPlate guidelines (myplate.gov) offer a practical, U.S.-specific framework.
Stay consistently active: The CDC recommends at least 150 minutes of moderate-intensity aerobic activity per week for adults, plus muscle-strengthening activities at least 2 days per week.
Prioritize sleep: The CDC recommends adults get 7 or more hours of sleep per night. Poor sleep is linked to weight gain and hormonal imbalance.
Track weekly trends, not daily fluctuations: Body weight can vary by 1–5 lb daily due to water retention, sodium intake, and hormonal cycles. Weekly or monthly trends are more meaningful.
Set gradual, realistic goals: A rate of 1–2 lb per week is generally considered safe and sustainable by U.S. health authorities.
Consult a professional: A U.S.-licensed physician, registered dietitian nutritionist (RDN), or certified personal trainer can create a plan tailored to your health history and goals.

Frequently Asked Questions

For most adults aged 18 and older, a BMI between 18.5 and 24.9 is considered within the normal or healthy weight range, according to the CDC and WHO. This range applies broadly across adult age groups. However, physicians may advise older adults to maintain a slightly higher BMI as a health buffer during illness or recovery.

In the United States, BMI is most commonly calculated using the Imperial formula: BMI = (weight in pounds ÷ height in inches²) × 703. The metric formula — weight in kilograms divided by height in meters squared — produces the same result and is used interchangeably in clinical settings.

BMI is a useful screening tool but isn't perfectly accurate for everyone. It doesn't distinguish between fat and muscle, so athletes and very muscular individuals may show a high BMI despite low body fat. The CDC notes it can also be less reliable for older adults, pregnant women, children, and certain ethnic groups where body composition norms differ. U.S. doctors typically combine BMI with other assessments such as waist circumference and blood panels for a fuller picture.

According to the CDC, a BMI between 25.0 and 29.9 is classified as overweight. A BMI of 30 or above falls into the obese category, further divided into Class I (30–34.9), Class II (35–39.9), and Class III — sometimes called severe obesity — (40 and above). These thresholds are consistent across major U.S. health organizations including the CDC, NIH, and the American Medical Association (AMA).

BMI for children and teens (ages 2–19) is calculated the same way but interpreted using age- and sex-specific CDC growth chart percentile tables, not fixed adult cutoffs — because body composition changes significantly during growth. This calculator is designed for adults aged 18 and above. Parents and pediatricians should use the CDC's child and teen BMI calculator for minors.

BMI estimates whether someone is in a healthy weight range based on height and weight alone, while body fat percentage measures the actual proportion of fat tissue in the body. Two people with the same BMI can have very different body fat percentages depending on muscle mass, bone density, and fat distribution. U.S. clinicians often use DEXA scans, hydrostatic weighing, or skinfold measurements to assess body fat percentage more precisely when BMI is inconclusive.

There's no strict rule, but checking every few months — or whenever your weight changes noticeably — is generally sufficient to track general trends. Daily checks aren't necessary and can cause undue focus on minor fluctuations caused by water retention, sodium, or hormonal cycles. BMI is typically reviewed as part of a routine annual physical with your primary care physician.

About This Tool & Editorial Standards

Toolriz Health & Wellness Tools Team

Content reviewed for accuracy against CDC and WHO BMI guidelines

Last updated: June 2026

This BMI calculator applies the standard formula and classification ranges published by the CDC and WHO. All content is written and reviewed to reflect current, publicly available guidance from U.S. and international health authorities. This tool is provided for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment from a licensed U.S. healthcare provider.

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