Body Mass Index (BMI) Calculator

Estimated BMI

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Weight:

Examples: 70 kg or 154 lb; unit changes convert the current value.

Height:

Examples: 170 cm, 1.70 m, 67 in, or 5 ft 7 in.

BMI classification:

Choose WHO, Asia-Pacific, or NIH/CDC adult bands.

Age (years):

Optional; enter 20 or older for adult screening notes, or leave blank.

Sex:

Optional; choose female or male only if you want the waist-threshold comparison.

Waist circumference:

Optional; measure midway between lowest rib and hip after a normal exhale.

Target BMI:

Drag within the selected healthy BMI span; current target updates beside the slider.

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BMI range	Category	Weight at your height	Copy
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Use this adult BMI calculator to convert height and weight into body mass index, compare the result with common adult screening bands, and review related context such as BMI Prime, ponderal index, waist-to-height ratio, and target-weight estimates.

BMI is a screening measure, not a diagnosis. The calculator is most useful for adults who want a consistent numeric summary before discussing weight, waist, and health risk factors with a qualified clinician.

Adult BMI result placed on screening bands — BMI is a screening index that should be read with age, body composition, waist measures, and clinical context.

How to Use:

Enter weight and height using the units that match your measurements.
Select the adult classification standard you want to compare against.
Add age to flag cases where adult bands may not apply.
Optionally enter waist circumference and sex for waist-context notes.
Choose a target BMI to estimate the matching target weight and change from current weight.

Interpreting Results:

The headline BMI is the weight-to-height index. The classification label depends on the selected adult standard, so the same BMI can be placed differently under international, Asia-Pacific, or U.S. adult bands.

BMI Prime compares your BMI with 25. A BMI Prime below 1 is below that reference cutoff, while a value above 1 is above it. Ponderal index gives a height-cubed version of the same body-size relationship and can be useful when comparing people with very different heights.

Waist-to-height ratio and sex-specific waist notes add central-adiposity context, but they do not replace clinical evaluation. The healthy-weight span and target-weight estimate are arithmetic guides based on the selected BMI band.

Technical Details:

Formula Core:

BMI = \frac{Weight (kg)}{{Height (m)}^{2}}

BMIPrime = \frac{BMI}{25}

PonderalIndex = \frac{Weight (kg)}{{Height (m)}^{3}}

WaistToHeight = \frac{Waist (cm)}{Height (cm)}

TargetWeight = TargetBMI {Height (m)}^{2}

Weight is converted to kilograms and height to meters before calculation. The healthy-weight span multiplies the lower and upper BMI cutoffs in the selected standard by height squared. The target BMI is constrained to the selected healthy range before target weight and weight-change values are shown.

Adult BMI categories use cutoff bands rather than individual body-composition measurement. The Asia-Pacific option uses lower overweight and obesity action thresholds than the general WHO adult standard. Waist-to-height ratio is grouped into lower, elevated, and high central-adiposity context bands, and sex-specific waist notes use common adult thresholds when sex is provided.

The calculator flags inputs that fall outside typical adult ranges, and it warns when age is under 20 because child and teen BMI is interpreted with age- and sex-specific percentiles.

Limitations and Safety Notes:

BMI does not directly measure body fat, muscle mass, bone density, pregnancy status, edema, or fat distribution.
Adult BMI bands are not appropriate for children and teens.
People with athletic builds, older adults, pregnant people, and those with medical conditions should interpret BMI with professional guidance.
Use the result as a screening conversation starter, not as a diagnosis or treatment plan.

Worked Examples:

Metric entry: A person weighing 72 kg at 1.75 m has BMI 72 / 1.75 squared, or 23.5. Under the general WHO adult bands, that falls in the reference range.

Target weight: At 1.70 m, a target BMI of 24 corresponds to 24 times 1.70 squared, or about 69.4 kg.

Waist context: A 90 cm waist at 170 cm height gives a waist-to-height ratio of 0.53, which is above 0.50 and should be read alongside other health factors.

FAQ:

Why does the category change when I switch standards?

Different adult standards use different cutoff bands. The BMI number stays the same, but the category label can change.

Is BMI accurate for athletes?

BMI can overstate risk for people with high muscle mass because it does not distinguish fat mass from lean mass.

Why include waist-to-height ratio?

Waist-to-height ratio adds central-adiposity context, which BMI alone cannot show.

Can this calculate BMI for a child?

No. Children and teens should be interpreted with BMI-for-age percentiles rather than adult bands.

Glossary:

BMI: Body mass index, calculated from weight divided by height squared.
BMI Prime: BMI divided by 25.
Ponderal index: Weight divided by height cubed.
Waist-to-height ratio: Waist circumference divided by height.
Target BMI: A selected BMI used to estimate the matching body weight.

References:

Adult BMI Categories, Centers for Disease Control and Prevention.
Identifying and assessing overweight, obesity and central adiposity, NICE guideline NG246.
Appropriate body-mass index for Asian populations and its implications for policy and intervention strategies, WHO Expert Consultation via PubMed, 2004.