Calculate your Body Mass Index (BMI), BMI Prime, healthy weight range and Ponderal Index for adults, using US, metric or custom units.
Google AdSense Banner
This area will contain advertisements after approval.
Google AdSense Banner
This area will contain advertisements after approval.
Body Mass Index (BMI) is a simple screening measure that estimates whether your weight is in a healthy range relative to your height. It's calculated as weight divided by height squared, and is widely used by healthcare providers, researchers and public health organizations as a quick, low-cost starting point for assessing weight status across large populations.
BMI doesn't measure body fat directly, and this calculator is intended for adults aged 18 and over, it doesn't use the separate age- and sex-specific percentile charts used for children and teenagers.
A BMI below 16 is classified as Severe Thinness; 16 to 17 as Moderate Thinness; 17 to 18.5 as Mild Thinness; 18.5 to 25 as Normal weight; 25 to 30 as Overweight; 30 to 35 as Obese Class I; 35 to 40 as Obese Class II; and 40 or above as Obese Class III.
These thresholds are the standard adult BMI classification used internationally, extending the commonly cited 'underweight / normal / overweight / obese' categories into finer bands that better distinguish mild from severe cases at both ends of the scale.
Carrying excess weight, particularly over a sustained period, is associated with an increased risk of several health conditions.
Increased risk of type 2 diabetes, as excess body fat contributes to insulin resistance.
Higher risk of high blood pressure and cardiovascular disease, including heart attack and stroke.
Greater strain on joints, particularly the knees and hips, which can contribute to osteoarthritis.
Increased risk of certain cancers, including breast, colon and endometrial cancer.
Higher likelihood of sleep apnea and other breathing difficulties during sleep.
Having too little body weight relative to height carries its own set of health risks, distinct from those of excess weight.
Weakened immune function, making infections more difficult to fight off.
Nutrient deficiencies, since low body weight can reflect inadequate intake of essential vitamins and minerals.
Reduced bone density and higher fracture risk, particularly in older adults.
Fertility issues, as very low body fat can disrupt hormone levels involved in reproduction.
Increased risk of anemia and fatigue from insufficient caloric or nutritional intake.
BMI is a screening tool, not a diagnostic one, it doesn't distinguish between fat mass and lean muscle mass. A muscular athlete can have a high BMI without carrying excess body fat, while someone with a 'normal' BMI could still have a high body fat percentage and low muscle mass, a pattern sometimes called 'normal weight obesity.'
BMI also doesn't account for where fat is distributed on the body, even though abdominal fat carries different health risks than fat carried elsewhere. It doesn't factor in bone density, overall body frame, or ethnicity-related differences in body composition that some research suggests affect the health risks associated with a given BMI.
For adults, this calculator applies a single set of thresholds. It does not include the CDC's separate growth-chart-based percentile method used to assess BMI in children and adolescents, since body composition changes substantially during growth and requires age- and sex-specific reference curves rather than fixed adult thresholds.
In SI (metric) units: BMI = weight (kg) ÷ height (m)². For example, someone weighing 70 kg at a height of 175 cm (1.75 m) has a BMI of 70 ÷ (1.75 × 1.75) = 70 ÷ 3.0625 ≈ 22.9, which falls in the Normal category.
In USC (imperial) units: BMI = 703 × weight (lb) ÷ height (in)². The constant 703 converts pounds and inches into the equivalent metric result without you needing to convert units yourself. For example, someone weighing 154 lb at a height of 68.9 in gets 703 × 154 ÷ (68.9 × 68.9) = 108,262 ÷ 4,747.2 ≈ 22.8, matching the metric result above (154 lb ≈ 70 kg, 68.9 in ≈ 175 cm) within normal rounding.
BMI Prime is BMI divided by 25 (the upper bound of the Normal BMI range), giving a simple ratio to the upper healthy-weight threshold. A BMI Prime of exactly 1.0 means your BMI is exactly 25; values below 1.0 mean your BMI is below 25, and values above 1.0 mean it's above 25.
BMI Prime uses its own classification: below 0.64 is Severe Thinness, 0.64 to 0.68 is Moderate Thinness, 0.68 to 0.74 is Mild Thinness, 0.74 to 1.0 is Normal, 1.0 to 1.2 is Overweight, 1.2 to 1.4 is Obese Class I, 1.4 to 1.6 is Obese Class II, and above 1.6 is Obese Class III, mirroring the standard BMI bands rescaled around 25.
The Ponderal Index is a related measure that divides weight by height cubed rather than height squared: PI = mass ÷ height³. In SI units, mass is in kilograms and height in meters, giving a result in kg/m³, typically in the range of about 11 to 15 for most adults.
Because it divides by height cubed instead of squared, Ponderal Index is considered less sensitive to a person's height than BMI is, some research suggests it's a more consistent measure across people of very different heights. The same underlying formula can be computed with weight in pounds and height in inches, using the appropriate unit conversion, and produces the same physical result once expressed in consistent units.
Treating BMI as a direct measurement of body fat, it's a weight-to-height ratio only, a muscular person and a person with high body fat can share the same BMI despite very different body compositions.
Comparing a child's or teenager's BMI against these adult thresholds, that requires the separate age- and sex-specific percentile method this calculator doesn't provide.
Mixing units accidentally, entering height in inches while selecting the metric formula (or vice versa) produces a BMI far outside any realistic range without an obvious error message pointing to the cause.
A BMI between 18.5 and 25 is generally classified as Normal weight for most adults. This calculator also breaks down BMI further into eight bands, from Severe Thinness to Obese Class III, for more detail than the four-category version.
BMI is a general screening tool and does not account for muscle mass, bone density, fat distribution, or body composition, so it may not be fully accurate for athletes, older adults, or people with an unusually muscular or lean build. It's a useful starting point, not a diagnosis.
BMI Prime is your BMI divided by 25, expressing how your BMI compares to the upper bound of the Normal range as a simple ratio. A BMI Prime under 1.0 means your BMI is below 25; over 1.0 means it's above 25.
The Ponderal Index divides weight by height cubed instead of height squared (as BMI does). This makes it less sensitive to height differences between people, and it's sometimes used as an alternative or complement to BMI in research settings.
No, this calculator is designed for adults aged 18 and over. Children and adolescents require a different, age- and sex-specific percentile-based method (such as the CDC growth charts), which isn't included here.
Age and gender don't change how BMI itself is calculated, they're used only to show general, non-diagnostic context notes, for example, that older adults and women tend to carry more body fat than younger adults or men at the same BMI.
The healthy weight range is the span of weights that would produce a BMI between 18.5 and 25 at your entered height, calculated by solving the BMI formula for weight at each of those two BMI values.
Yes, select 'Other' in the unit toggle to choose your height unit (centimeters, meters, inches or feet) and weight unit (kilograms, pounds or stone) independently.
Calorie Calculator for Weight Goals
Calculate your daily calorie target to lose, maintain or gain weight.
Google AdSense Banner
This area will contain advertisements after approval.