Height Calculator
Calculate a height percentile with WHO and CDC reference data and convert measurements between centimeters and feet and inches.
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BMI Calculator
Calculate BMI with standard or metric measurements, adult category ranges, and age- and sex-aware context for children and teens.
BMI category chart
Adult BMI ranges for age 20+Interpret your BMI result
BMI compares weight with height and places the result in a screening category. It can be useful for population-level guidance and quick checks, but it does not directly measure body fat, fitness, or overall health.
Inputs that matter most
- Height and weight: small entry errors can noticeably change the BMI value.
- Age: adult categories apply at age 20 and older; children and teens use BMI-for-age percentiles.
- Sex: used for child and teen percentiles and the rough body fat estimate.
- Units: make sure height and weight are entered in the selected measurement system.
Common mistakes
- Treating BMI as a diagnosis instead of a screening measure.
- Using adult BMI categories for children or teens.
- Ignoring body composition, such as higher muscle mass or lower muscle mass.
- Comparing results without considering age, pregnancy, health history, or clinical context.
When this estimate can be misleading
BMI can be misleading for athletes, older adults, pregnant people, people with significant muscle loss, and anyone whose body composition differs from the assumptions behind height-weight screening categories.
Scenarios to try
- Switch between standard and metric units to confirm the same result.
- Check that height is entered as total feet and inches, not decimal feet.
- For ages 2 through 19, focus on the BMI-for-age percentile category.
- Use waist measurement, body composition, and clinician guidance for a fuller health picture.
Next-step utilities
How to use this BMI calculator
Enter age, sex, height, and weight in standard or metric units to calculate BMI and review category guidance.
- Choose standard or metric units.
- Enter height, weight, age, and sex.
- Review the BMI value, adult category table, and any age-specific guidance.
- Use the body fat estimate as a rough screening estimate only.
BMI Calculator features
- Calculate BMI from standard or metric height and weight inputs.
- Enter age in years and months for child and teen guidance.
- Choose sex for BMI-for-age percentile context.
- Switch between standard and metric measurement systems.
- Review adult BMI categories for age 20 and older.
- Review age-specific guidance for children and teens.
- See a BMI category chart update with the entered measurements.
- Review a rough body fat estimate alongside the BMI screening result.
What BMI means
Body mass index compares weight with height.
Adult BMI categories apply to people age 20 and older. For ages 2 through 19, BMI is interpreted using CDC age- and sex-specific percentiles.
BMI is a screening measure, not a diagnosis. A clinician can consider body composition, health history, and other measurements for personal guidance.
BMI formulas and data sources
BMI is calculated from height and weight, then interpreted using adult ranges or age-specific child and teen references.
BMI = \frac{weight_{lb}}{height_{in}^2} \cdot 703
BMI = \frac{weight_{kg}}{height_m^2}
BF\% = 1.2 \cdot BMI + 0.23 \cdot age - 10.8 \cdot s - 5.4
Used for age 20 and older. s is 1 for male and 0 for female.
BF\% = 1.51 \cdot BMI - 0.7 \cdot age - 3.6 \cdot s + 1.4
Used for ages 2 through 19. s is 1 for male and 0 for female.
Adult BMI categories use CDC adult BMI ranges. For ages 2 through 19, CDC BMI-for-age guidance uses percentiles based on age and sex.
The body fat percentage estimate uses published BMI, age, and sex equations from Deurenberg, Weststrate, and Seidell.
BMI calculator FAQ
What are the adult BMI categories?
Adult BMI categories are underweight below 18.5, healthy weight from 18.5 to less than 25, overweight from 25 to less than 30, and obesity at 30 or higher.
Why enter age and sex?
Adult BMI categories use the same BMI cutoffs for males and females, but child and teen interpretation uses sex-specific BMI-for-age percentiles. Age and sex also power the optional body fat estimate shown in the result panel.
Is BMI a diagnosis?
No. BMI is a screening measure. A clinician can consider body composition, health history, and other measurements for personal guidance.
Interpret BMI with the right context
BMI is useful as a population-level screening measure because it needs only height and weight. It does not directly measure body fat, muscle, bone, fat distribution, fitness, or metabolic health. Two people with the same BMI can have different body composition and health histories. Treat the displayed category as a prompt for context, not a diagnosis.
Adult categories apply from age 20. Children and teenagers are still growing, so their BMI is compared with age- and sex-specific reference data. The CDC BMI FAQ explains this difference and recommends BMI-for-age percentiles for ages 2 through 19. A percentile describes position in a reference distribution; it does not by itself explain a child's growth pattern.
Measurement error can move a result near a category boundary. Measure height without shoes and weight on a stable scale, then repeat under similar conditions if you are tracking change. Normal daily shifts in hydration and food weight can affect the scale. A single reading is less informative than a consistent pattern reviewed with other health information.
The body-fat estimate shown here is even rougher than BMI because it applies a population equation rather than measuring tissue. Do not use it to set a treatment target or evaluate an athlete, pregnancy, edema, or a condition that changes body composition. A clinician can consider waist measures, growth history, laboratory results, medicines, symptoms, and family history.
If a result worries you, avoid making a rapid diet or exercise change from the number alone. Discuss the measurement with a qualified health professional, especially for a child or teen. For a unit check before recalculating, the height calculator converts between centimeters and feet and inches.
When tracking BMI over time, keep the method consistent and focus on the broader trend. A change in the number does not explain whether weight came from fat, muscle, fluid, pregnancy, growth, or recovery from illness. Medicines and medical conditions can also affect weight. Bring the measurements and their dates to a clinician when the change is unexpected, rapid, or accompanied by symptoms.
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