Body Adiposity Index (BAI) Calculator

About this calculator

Estimate body adiposity using only your hip circumference and height. No scale needed, with measurement guidance and clear limits on individual accuracy.

BAI is an anthropometric estimate and should not be interpreted as an exact body-fat measurement or medical diagnosis. This calculator reports a neutral score, without health categories or a body-fat target.

How to use the BAI Calculator

Select Metric or US / Imperial. Enter hip circumference and height, confirm that you are 18 or older, then select Calculate BAI. The example inputs are 95 cm and 175 cm; they are not recommended measurements.

After the first calculation, valid measurement edits update the result immediately. Invalid entries replace the estimate with an explanation. Unit switching converts existing values; correct invalid entries before switching. Open How to measure for tape-position guidance. Weight is requested only if you expand the optional BMI comparison.

What is Body Adiposity Index?

Bergman and colleagues proposed Body Adiposity Index in 2011 as a way to approximate percentage adiposity without weighing. The original work developed the index in the adult BetaGene dataset and compared it with DXA in the TARA dataset.

That proposal is distinct from later validation. A useful correlation in a study does not establish accurate estimates for each person. This page uses BAI score as its main label and avoids displaying a percentage as if body fat had been directly measured.

BAI formula

BAI = hip circumference (cm) ÷ height (m)^1.5 − 18

Units are essential: hip circumference is in centimeters, while height is in meters. Height in centimeters is divided by 100 first. For imperial measurements, hip inches are multiplied by 2.54 and total height inches by 0.0254. The same formula then applies; there is no separate approximated imperial equation.

The engine retains full numerical precision. Results display one decimal place for readability, which does not imply that the measurement or estimate is that accurate.

Why BAI does not require body weight

No scale needed: the BAI formula uses only hip circumference and height. Weight is neither inferred nor required. This makes the arithmetic possible when a scale is unavailable, but convenience does not remove its accuracy limitations.

Age and sex do not appear in the formula. Adult confirmation defines this tool’s scope; it is not a substitute for assessing whether the equation is appropriate for an individual.

How to measure hip circumference

• Use a flexible, non-stretch measuring tape.
• Stand naturally with feet together and weight evenly supported.
• Measure around the widest part of the hips and buttocks, rather than the waist.
• Keep the tape horizontal, snug and flat, without compressing skin or including bulky clothing.
• Repeat if uncertain and check placement each time.

The original TARA protocol used the maximum backward extension of the buttocks in a horizontal plane and recorded the average of three readings. CDC/NHANES also emphasizes horizontal alignment and a snug tape. Self-measurement can introduce placement and tension errors even when the formula is applied correctly.

How height is used

Measure standing height without shoes, upright against a suitable vertical surface. Imperial input separates whole feet from inches; inches must be at least zero and less than 12. Height is converted to meters internally and reused for BMI if you choose that comparison.

At fixed hip circumference, increasing height reduces BAI because height raised to 1.5 is in the denominator. This is a mathematical relationship, not advice to change body measurements. Repeated unit toggles retain the canonical measurements rather than recalculating from rounded display values.

BAI vs BMI

BAI uses hips and height to estimate adiposity. BMI uses weight relative to height: BMI = weight (kg) ÷ height (m)². CDC describes BMI as a screening measure, not a direct body-fat measurement; it cannot separate fat from muscle and bone.

Neither value provides a complete body-composition or health assessment. BAI is not categorically superior to BMI. Their numerical values have different meanings and should not be averaged or treated as competing diagnoses.

The optional tool asks only for weight and uses the height already entered. Pounds convert using 1 lb = 0.45359237 kg. No BMI categories are shown: the 18+ confirmation includes ages 18–19, for whom CDC uses age- and sex-specific interpretation rather than its 20+ adult categories. Closing the comparison clears weight.

How accurate is BAI?

Individual error can be substantial. A 2018 systematic review of 19 adult studies comparing BAI with DXA found poor agreement and large individual errors. It concluded that BAI had limited capacity to estimate body-fat percentage and did not recommend it for determining that percentage in adults.

BAI can overestimate in some people and underestimate in others. Validation performance varies across populations and body compositions; an estimate close to a group average may still be far from one individual’s reference result. A score from this tool should not drive treatment or be treated as an exact percentage.

BAI limitations

This tool is for adult educational use, not pediatric, pregnancy, breastfeeding or therapeutic nutrition assessment. It does not diagnose obesity, underweight, metabolic health or disease risk. Athletes and people with unusual body proportions should not assume the formula accurately represents their composition.

The supported entry bounds are hip 40–200 cm and height 100–250 cm, with optional BMI weight 20–400 kg. These are broad engineering limits for input checking, not clinically validated BAI ranges or definitions of a normal body. Mathematically valid extreme combinations are accepted but may produce uninterpretable scores.

If a formula output is below 0 or above 100, it is shown explicitly as raw output outside the interpretable adiposity range. It is not clamped into a plausible-looking estimate and no visual marker is plotted. Recheck measurements and units. Even outputs within 0–100 are not validated individual body-fat measurements.

Sex is omitted because it does not change the original equation and the reviewed evidence does not establish broadly applicable sex-specific BAI diagnostic bands. No universal healthy/overfat/obese zones are used. The neutral 0–100 display is illustrative, not a reference standard, confidence interval or goal.

Why body-composition estimates can differ

More direct body-composition methods can produce estimates different from BAI. DXA and professionally performed assessments use different measurements and assumptions; they are not perfectly error-free either.

Measurement protocol, equipment, body proportions and the population in which a model was studied all affect comparisons. A discrepancy does not by itself establish disease or a need for medical testing. Discuss relevant health concerns with a qualified professional rather than trying to reconcile these numbers through dieting or treatment changes.

Worked example

For hip circumference 95 cm and height 175 cm, first convert height to 1.75 m:

95 ÷ (1.75^1.5) − 18 = 23.036142783859

The displayed BAI score is 23.0. Both values are generated by the same engine as the interactive form. This is a BAI estimate, not a direct measurement of body-fat percentage.

Body Adiposity Index FAQ

What is Body Adiposity Index?

BAI is an anthropometric index using hip circumference and height. It was proposed as an estimate of adiposity without body weight.

How is BAI calculated?

Divide hip circumference in centimeters by height in meters raised to 1.5, then subtract 18. Converting units before calculating is essential.

Does BAI require body weight?

No. The main calculator requires hips and height only. Weight is optional for a separate BMI comparison.

Is BAI the same as body-fat percentage?

No. It was designed to approximate percentage adiposity, but it does not directly measure body fat. This tool displays a BAI score rather than an apparently precise percentage.

How accurate is BAI?

Individual accuracy is limited. Later adult validation evidence found large errors compared with DXA, so a score should not be treated as an exact body-fat result or diagnosis.

How should I measure my hips?

Place a flexible tape around the widest hips/buttocks area, keep it level and snug without compressing skin, and repeat if uncertain. Avoid measuring the waist instead.

Does sex change the BAI formula?

No. The original equation has no sex term. This tool omits sex and does not apply population-specific interpretation tables as universal categories.

What is the difference between BAI and BMI?

BAI uses hips and height; BMI uses weight and height. Neither directly measures body-fat percentage. The optional comparison reports BMI without diagnostic categories.

Can athletes use BAI accurately?

Athletic status does not guarantee accuracy. Muscle distribution and body proportions can differ from those in validation samples; no athlete-specific correction is applied.

Does BuzCalculator save my measurements?

No automatic saving or input-sharing URL is used. Values stay in tab memory and clear on refresh. Copy result exports generated outputs only when chosen; closing BMI clears its weight entry.

Sources and methodology review

Methodology reviewed September 28, 2026. The original paper establishes provenance; later validation informs the prominent uncertainty statements. This is an editorial review, not clinical approval.

• Bergman et al. (2011): A better index of body adiposity (opens in a new tab)
• Cerqueira et al. (2018): Validity of the Body Adiposity Index in Predicting Body Fat in Adults — systematic review (opens in a new tab)
• CDC: About Body Mass Index (opens in a new tab)
• CDC/NHANES: Anthropometry Procedures Manual (2021), hip circumference protocol (opens in a new tab)
• Bergman et al.: Original methods and measurement protocol (opens in a new tab)

Input bounds and visualization endpoints are product choices, not diagnostic standards endorsed by these sources.