Adult BMI Calculator

Adult BMI calculator for women and men

For adults age 20 and older, body mass index is weight in kilograms divided by height in meters squared. The same standard BMI formula and adult category boundaries are used for women and men. Age and profile do not change the BMI number itself. In this calculator, age and profile are used only when the optional population-based body-fat estimate is requested.

The adult BMI calculator accepts pounds with feet and inches, kilograms with centimeters, or stone and pounds with feet and inches. Regardless of the selected unit system, values are converted to kilograms and meters before the result is calculated. The report displays both U.S. and metric equivalents so the calculation can be checked independently.

Adult results include BMI, the standard adult category, the healthy-range weight interval for the entered height, BMI Prime, Ponderal Index, the selected target-BMI weight, distance from the standard healthy range and a height-adjusted comparison formula. Optional waist input adds waist-to-height ratio without replacing the BMI result.

BMI chart and healthy-weight range

The interactive BMI chart marks the current result against the standard adult category boundaries: below 18.5, 18.5 through 24.9, 25.0 through 29.9, 30.0 through 34.9, 35.0 through 39.9, and 40.0 or greater. These correspond to underweight, healthy weight, overweight, Class 1 obesity, Class 2 obesity and Class 3 obesity.

A second table converts common BMI levels into the exact weight required at the entered height. This makes the BMI chart practical for reverse calculations. For example, rather than asking only “what is my BMI,” a visitor can enter a target BMI and see the corresponding weight in pounds, kilograms and stone. The target is a mathematical scenario, not a recommendation.

The healthy-weight interval is found by solving the BMI formula at 18.5 and 24.9. Since this range depends on height, two people with different heights will receive different weight intervals even when the category boundaries are identical.

BMI calculator for women, men and older adults

Searches for a BMI calculator for women and a BMI calculator for men often imply that separate formulas are required. The standard adult BMI calculation does not change by gender. However, two adults with the same BMI can have different body composition, muscle mass, fat distribution, age-related changes and health history. That is why the result is presented as a screening measure rather than a direct body-fat test.

The optional estimated body-fat percentage uses a published population equation containing BMI, age and profile. It is displayed separately and clearly labeled as an estimate. It is not used to alter the BMI category. Athletes, highly muscular adults, older adults, pregnant people and anyone with unusual body composition may need more direct assessment methods.

BMI thresholds do not automatically become stricter or looser with adult age. The age field is therefore not used to modify the standard adult category. Older adults may still need additional context because the same BMI can correspond to different proportions of fat and lean tissue at different ages.

Child and teen BMI percentile calculator

Children and teens cannot be interpreted with adult BMI categories because they are still growing. The child and teen mode calculates BMI first, then compares it with an age-specific boys' or girls' CDC reference chart. The result includes BMI percentile, extended z-score, weight category, percentage of the age-specific 95th percentile and the 5th, 50th, 85th, 95th and severe-obesity reference values.

For completed years and months, the calculator uses the midpoint of the completed month, matching the CDC recommendation when an exact age in days is unavailable. When date of birth and measurement date are supplied, age is calculated in days and converted to average months before the growth-chart parameters are interpolated.

Percentiles through the 95th use the CDC LMS method. Higher values use the 2022 Extended BMI-for-age method with age- and chart-specific sigma parameters. Severe obesity is identified when BMI is at least 120% of the 95th percentile or at least 35 kg/m². The growth chart plots the calculated point with major reference curves, but a single point cannot show a child's growth trajectory.

BMI formula in pounds, kilograms and stone

Suppose an adult weighs 180 pounds and is 5 feet 10 inches tall. The height is 70 inches. The U.S. calculation is 703 × 180 ÷ 70², producing approximately 25.8. The equivalent metric inputs are about 81.65 kilograms and 1.778 meters, which produce the same answer apart from rounding.

BMI Prime divides BMI by 25. A BMI Prime of 1.00 corresponds to BMI 25, while 0.90 corresponds to BMI 22.5. Ponderal Index divides kilograms by height in meters cubed. It is included as a supplemental height-normalized measure and does not replace standard BMI categories.

What BMI can and cannot tell you

BMI is a calculated screening measure of weight relative to height. It does not directly measure body fat percentage, visceral fat, muscle mass, bone density, fitness, blood pressure, blood glucose, cholesterol, nutritional status or the cause of a person's weight. A result within the healthy category does not guarantee good health, and a result outside it does not by itself diagnose disease.

Measurement quality matters. Height should be measured without shoes and weight should be measured on a stable scale. Small input differences can move a result near a boundary. The calculator therefore keeps full precision internally and rounds only the displayed answer.

For children and teens, professional interpretation should consider repeated measurements over time rather than one isolated percentile. For adults, healthcare providers may combine BMI with history, examination, laboratory findings, waist measurements and direct body-composition methods. This calculator is educational and is not a substitute for professional medical advice.