Used in formula calculations. Select the option that matches your physiology for most accurate body composition results. If you have questions, consult a healthcare provider.
Required for women's Navy Method BF%; enables WHR and body shape classification
Athlete mode active — BMI may overestimate body fat for muscular individuals
Your Results
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Update your measurements above to recalculate
18.52530
UnderweightNormalOverweightObese
Healthy Weight—
Estimated Body Fat %—
Advanced metrics
BMI Prime—
Ponderal Index—
Lean Mass—
Fat Mass—
Waist-to-Height—
Rel. Fat Mass (RFM)—
Ideal Weight Range—
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Body-composition estimates are population-based approximations, not direct measurements. Deurenberg uses BMI, age, and sex; Navy uses circumferences; RFM uses height, waist, and sex. These methods may be unreliable in pregnancy, high muscle mass, or medical conditions.
Enable waist & hip measurements to see your body shape classification.
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Body Composition Breakdown
Estimated Body Fat %—
Fat Mass—
Lean Mass—
BMI Prime—
Lean mass includes muscle, bone, organs, and water. Fat mass is estimated using the Deurenberg formula (based on BMI, age, and sex). See the Body Composition tab for a comparison of all estimation methods.
Enter your measurements to see body composition.
Ideal Body Weight — 4 Formula Comparison
Ideal body weight formulas were developed for clinical dosing. Your healthiest weight depends on muscle mass, frame size, and individual factors.
Formula
Year
Ideal Weight
vs. Current
Devine
1974
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Robinson
1983
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Miller
1983
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Hamwi
1964
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BMI vs. Your Age Group
Compare your BMI to population averages by age from NHANES data.
No entries yet. Log your first measurement above to start tracking your progress.
Date
Weight
BMI
Category
Understanding your BMI
BMI is a screening measure based on height and weight. It does not measure body fat directly or diagnose a health condition.
For adults 20 and older, standard categories are below 18.5, 18.5 to less than 25, 25 to less than 30, and 30 or higher. Categories alone cannot describe your overall health.
Muscle mass, pregnancy, aging, and medical conditions can affect interpretation. A clinician can consider your measurements alongside blood pressure, laboratory results, and medical history.
Higher BMI is associated with some health conditions at a population level. This calculator does not estimate your personal probability of diabetes, cardiovascular disease, or other illness.
BMI does not distinguish muscle from fat. Athletes, older adults, pregnant individuals, and some ethnic groups may need a different reference.
How do you calculate BMI?
BMI is calculated by dividing your weight in kilograms by your height in meters squared: BMI = weight(kg) / height(m)². For example, a person who is 5'10" (1.78m) and weighs 180 lbs (81.6 kg) has a BMI of 25.8, which falls in the overweight category.
Enter age, height, and weight for an adult 20 or older. BMI updates as you type. Sex affects only optional body-composition estimates.
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Add Optional Measurements
Open Optional body measurements to enter sex and optional waist, neck, and hip measurements for circumference-based estimates.
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Explore Body Composition
Switch to the Body Composition tab to compare three body fat estimation methods side-by-side and see your ideal weight from four clinical formulas.
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Understand BMI and track measurements
Read Understanding BMI for its limitations. Goals & History lets you compare hypothetical scenarios and save measurements in this browser.
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Reference
Formula & Methodology
3 formulas▸
Body Mass Index (BMI)
BMI = weight(kg) / height(m)²
WHO standard (Quetelet Index). For imperial inputs, the equivalent is (weight_lbs × 703) / height_in². Categories: Underweight <18.5, Normal 18.5–24.9, Overweight 25–29.9, Obese ≥30.
Waist-to-Height Ratio (WHtR)
WHtR = waist(cm) / height(cm) — healthy if < 0.5
Ashwell & Hsieh central obesity screen. A value under 0.5 is considered healthy for most adults; it is a stronger predictor of cardiovascular and metabolic risk than BMI because it specifically captures abdominal fat.
Woolcott & Bergman 2018. RFM uses only height and waist circumference and has a higher correlation with DEXA-measured body fat (r = 0.80) than BMI (r = 0.68), making it less susceptible to muscle-mass bias.
BMI = weight in kilograms / height in meters squared. For adults 20 and older, using standard CDC categories. Optional estimates and weight scenarios are educational; no health score or personal disease-risk rating is calculated.
Assumption: Height, weight, and circumference measurements are current and taken consistently, preferably without heavy clothing and with the same units selected in the calculator.
Assumption: Categories apply only to adults 20 and older; younger users are directed to pediatric calculators.
Assumption: Body-composition formulas estimate population averages and do not directly measure fat mass, lean mass, bone density, or visceral fat.
Limitations & guidance
BMI and related screening formulas can misclassify children and teens, pregnant or recently pregnant people, older adults with low muscle mass, and athletes or very muscular users.
Body composition, ethnicity, medication use, edema, eating disorders, disability, and clinical history can change what a weight or circumference result means.
Do not use this result by itself to diagnose obesity, malnutrition, cardiovascular risk, or eligibility for medication, surgery, or a treatment plan.
This tool is intended solely for educational and informational purposes. Body Mass Index (BMI) is a population-level screening metric and does not diagnose individual body composition, visceral adiposity, or metabolic health. Consult a qualified healthcare professional or registered dietitian before initiating weight management programs or interpreting clinical risk.
Professional guidance: BMI Calculator is a wellness screening tool, not medical advice. Use it as a starting point and discuss weight, body-composition, pregnancy, adolescent, athletic, or health-condition concerns with a licensed healthcare professional.
BMI ↗Body Mass Index — weight in kilograms divided by the square of height in meters. It is a population-level screening tool, not a direct measure of body fat or individual health.
RFM ↗A population-based body-fat estimate using height, waist, and sex. It does not directly measure fat or determine an individual’s health.
WHtR ↗Waist circumference divided by height in the same units. It describes body proportions and should be interpreted alongside other health information.
IBW ↗Ideal Body Weight — clinically derived height-and-sex-based target weights from formulas by Devine, Robinson, Miller, and Hamwi, used primarily in pharmacology and dietetics.
Screening ↗An initial assessment that can help identify when further evaluation may be useful. It is not a diagnosis or a treatment plan.
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Scenarios
Real-World Examples
3 worked examples▸
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Sarah — Recreational Runner
Active Adult
Height 5'6" (168 cm)Weight 140 lbs (63.5 kg)Waist 28 in (71 cm)Age 28 yearsBMI 22.6 — Normal
Sarah's BMI sits solidly in the normal range, and her WHtR of 0.42 — well under the 0.5 threshold — confirms healthy central fat distribution. The Deurenberg body fat estimate of roughly 25% is appropriate for an active woman, and her lean.
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Mike — Sedentary Office Worker
Office Worker
Height 5'10" (178 cm)Weight 210 lbs (95.3 kg)Waist 38 in (96.5 cm)Age 42 yearsBMI 30.1 — Obese Class I
Mike's BMI just crossed into the obese range, but his WHtR of 0.54 tells the more important story — above 0.5 indicates elevated central adiposity with higher cardiovascular and metabolic disease risk.
Helen’s BMI is in the adult overweight category. For older adults, muscle mass and clinical history also matter; BMI alone does not determine an appropriate personal weight target.
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Reference
Cite This Calculator
APA & MLA▸
Use either format to cite this calculator in a paper, report, or resource list.
BMI relates weight to height. Use it as a starting point for understanding your measurements, alongside their context and limitations.
What this tool calculates
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BMI is weight in kilograms divided by height in meters squared, expressed in kg/m². Standard CDC categories apply to adults 20 and older. They do not change by sex; this page directs younger users to pediatric calculators that interpret BMI by age and sex. Measure height without shoes and use a consistent scale. Switching units changes the display, not the physical measurement.
What BMI cannot tell you
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BMI does not distinguish fat from muscle or describe where fat is stored. Pregnancy, aging, muscle mass, and medical conditions can affect interpretation. A clinician can consider your measurements with blood pressure, laboratory results, and medical history. This calculator does not predict illness or assign a health score. A category is a screening description, not a judgment about a person or a prescription to change weight.
Optional estimates and history
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Deurenberg estimates body fat from BMI, age, and sex; Navy uses circumferences; RFM uses height, waist, and sex. These population-based approximations depend on measurement technique. Reference-weight formulas are not personal targets. History is saved in this browser when storage is available. Weight scenarios assume a hypothetical constant rate; they are not recommended diets, and actual weight change is not linear. Review the cited methods and discuss clinical questions with a qualified professional.
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Questions
Frequently Asked Questions
6 questions▸
Who is this calculator for?+
Adults 20 and older. Ages 2–19 need age- and sex-specific interpretation; use our child or teen BMI calculator.
Does BMI diagnose my health?+
No. BMI is a screening measure. It does not directly measure body fat or determine your individual risk of disease.
What are the adult BMI categories?+
Below 18.5: underweight; 18.5 to less than 25: healthy weight; 25 to less than 30: overweight; 30 or higher: obesity. This page uses standard CDC categories.
How reliable are body-fat estimates?+
Deurenberg, Navy, and RFM are population-based prediction methods. Measurement technique and individual physiology affect accuracy. They are not direct measurements and may be unreliable in pregnancy or high muscle mass.
Where are my measurements saved?+
Measurements and history are saved in this browser when storage is available. Shared URLs include measurements; share them only with people you choose. Reset clears the current form; Clear History removes saved history.
Are goals a treatment plan?+
No. Goals are hypothetical constant-rate comparisons. The calorie arithmetic is a simplified model, not a recommended diet; actual weight change is not linear.
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