Covert Bailey body fat calculator

The path is fully offline: no network, no random seed, and no clock, so homework checkers, coaching apps, and prepaid API clients receive identical JSON for the same inputs every time. Missing fields, non-numeric values, and non-positive girths fail with invalid_input and are not billed. Use the free browser tool for field checks and progress logs, or call the API at $0.002 per successful item when pipelines need a stable Covert Bailey contract without re-implementing age-band coefficients.

What the Covert Bailey method measures and how the four girths become percent fat

The response echoes sex, age, the age band label, each girth converted to inches, body fat percent, the method tag covert_bailey, a formula string, and the precision used for rounding.

Input contract, validation rules, and reading the response fields

Male requests must also supply waist and forearm. Female requests must also supply thigh and calf. Optional unit defaults to inches and also accepts inch, inches, cm, centimeter, and centimeters; centimetre values are divided by two point five four before the formula runs so the arithmetic always matches Bailey’s inch-native published forms. POST a JSON object with required sex, age, hips, and wrist, plus the two additional sites that complete the sex-specific quartet. Sex accepts male or female and common short forms such as m, f, man, and woman after case folding; aliases gender and sex_at_birth are also recognized. Age is a positive finite number of years, with aliases age_years and years; values through thirty inclusive use the younger coefficient set, and values above thirty use the over-thirty set. Optional precision, with aliases decimals and dp, chooses zero through twelve decimal places for rounded outputs and defaults to two. Missing fields, empty strings, non-finite numbers, zero or negative age, and zero or negative girths raise invalid_input naming the offending rule; those failures do not consume prepaid balance. On success you receive body_fat_percent for display and logging, age_band as thirty_and_under or over_thirty, unit_input reflecting the unit you sent, each used site as a starred inches field such as waist_in or thigh_in, method always set to covert_bailey, and formula so downstream code can audit coefficients without hard-coding them. Do not confuse this endpoint with the US Navy circumference calculator or with Jackson-Pollock skinfold endpoints: those use different landmarks, different mathematics, and live under separate product pages.

Where a Covert Bailey girth API earns its keep and how pricing works

Coaches and personal trainers use a Covert Bailey body fat calculator when clients already keep a measuring tape in the gym bag and need a reproducible four-site estimate without buying calipers or booking a Bod Pod session. Exercise-physiology courses assign circumference labs and need an oracle that rejects non-positive girths instead of inventing a silent zero-percent result. Progress trackers benefit from the age-band split: a client who crosses thirty years old automatically switches coefficients without a silent formula mismatch. Keep clinical expectations honest—this is not a diagnostic medical device—and pair consistent tape technique with the numbers so site-placement errors are not mistaken for formula bugs. On this page the work runs entirely in your browser; through the API each successful lookup costs $0.002, validation failures are not charged, and nothing is stored after the response returns. That split matches the rest of the KIT tier-A catalog: free interactive exploration and a priced, identical automation path. If your workflow already stores body-fat percent and only needs lean mass, fat mass, or basal metabolic rate, use the dedicated composition endpoints rather than re-deriving those quantities here.