Jackson-Pollock 3-site body fat for women
Estimate a woman's body fat from three caliper skinfolds and her age: 18 mm at the triceps, 16 mm above the hip bone and 24 mm at the front thigh at age 30 give 23.4735% with the 1980 Jackson-Pollock equation. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Triceps
- 18
- Suprailiac
- 16
- Thigh
- 24
- Age
- 30
- Triceps mm
- 18
- Suprailiac mm
- 16
- Thigh mm
- 24
- Age (years)
- 30
This Jackson-Pollock three-site body fat calculator for women estimates body fat percentage from three caliper skinfolds in millimetres—triceps, suprailiac, and front thigh—plus age in years. The classic 1980 Jackson and Pollock equation first predicts body density from the sum of those sites and age, then converts density to percent fat with the Siri formula so you get a reproducible BF% without a scanner, DEXA booking, or proprietary app. A typical adult check might use eighteen millimetres at the triceps, sixteen at the suprailiac, twenty-four at the thigh, and age thirty, yielding a density near one gram per cubic centimetre and a mid-twenties body-fat estimate under published coefficients. The engine is fully deterministic: no network calls, no random sampling, and no date-dependent shortcuts.
What the three-site method measures and what you get
Skinfold calipers pinch a double fold of skin and subcutaneous fat at standard anatomical sites. For adult women the Jackson-Pollock three-site protocol uses the triceps (vertical fold on the back of the upper arm), the suprailiac (diagonal fold just above the iliac crest), and the front thigh (vertical fold on the anterior mid-thigh). Those three thicknesses in millimetres are summed; age in years enters as a separate linear term that reflects how density and fat distribution change across adulthood.
Body density is predicted with the published female three-site equation: one point zero nine nine four nine two one minus zero point zero zero zero nine nine two nine times the sum, plus zero point zero zero zero zero zero two three times the sum squared, minus zero point zero zero zero one three nine two times age. Percent body fat then follows Siri: four hundred ninety-five divided by density, minus four hundred fifty.
Where female three-site body fat estimates fit in practice and software
Coaches and athletes use Jackson-Pollock three-site estimates when tracking composition across a training block with a consistent caliper protocol, when comparing relative leanness without relying on scale weight alone, or when explaining why two women with similar body mass index can show very different skinfold sums. Students meet these equations in exercise physiology and kinesiology labs when textbooks introduce density methods before more expensive laboratory techniques.
Product teams call the same contract from scripts to seed deterministic test vectors for health dashboards, to normalize coach-entered millimetre values before composition charts, or to satisfy programming-challenge statements that demand a Jackson-Pollock women three-site result rather than a black-box app. Treat the output as an educational and planning estimate: technique, hydration, and site placement affect caliper readings, and clinical or research decisions should prefer multi-method body composition and a qualified professional when accuracy matters.
Pair this tool with lean-mass or calorie helpers when you need related anthropometrics, keep millimetres honest, and never mix inch-scale caliper readings without converting first.
What you can do with it
Coaching and training logs
Estimate female body fat from triceps, suprailiac, and thigh skinfolds plus age when tracking a consistent caliper protocol across training blocks.
Exercise physiology labs
Let students compute Jackson-Pollock three-site density and Siri BF% from measured millimetre folds without re-deriving coefficients by hand.
FAQ
What does the Jackson-Pollock 3-site women calculator cost?
It is free in your browser on this page.
Which formula is used?
Jackson-Pollock 1980 women three-site body density from triceps, suprailiac, and thigh (mm) plus age, then Siri BF% = (495 / density) − 450.
What happens if a skinfold or age is missing?
Triceps, suprailiac, thigh, and age are all required and must be finite positive numbers.
Does this replace DEXA or hydrostatic weighing?
No. It is a skinfold anthropometric estimate using published coefficients. Use laboratory composition methods when clinical accuracy is required.
What units should I use?
Skinfolds in millimetres and age in years. Convert inch-scale caliper readings to millimetres before calling so the coefficients apply correctly.
Related tools
For developers — API access
Everything on this page is available programmatically. This section is for teams who want to wire it into their own systems; everyone else can just use the tool above.
API endpoint
Prefer to automate it? One authenticated POST creates the task; the result comes back by webhook or a signed link. The same capability also runs here on the web, by email and from Telegram — and soon from our app too.
Call it from your stack
curl -X POST https://api.kit.forhosting.com/health/bodyfat-jp3-women \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"triceps":18,"suprailiac":16,"thigh":24,"age":30}'const res = await fetch("https://api.kit.forhosting.com/health/bodyfat-jp3-women", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"triceps": 18,
"suprailiac": 16,
"thigh": 24,
"age": 30
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/health/bodyfat-jp3-women",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"triceps": 18,
"suprailiac": 16,
"thigh": 24,
"age": 30
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/health/bodyfat-jp3-women", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"triceps":18,"suprailiac":16,"thigh":24,"age":30}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"triceps":18,"suprailiac":16,"thigh":24,"age":30}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/health/bodyfat-jp3-women", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"triceps": 18,
"suprailiac": 16,
"thigh": 24,
"age": 30
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "health.bodyfat_jp3_women",
"status": "queued",
"_links": {
"result": "/tasks/tsk_…/result"
}
}The API is asynchronous: the call returns a task_id immediately and the result arrives by webhook. Polling is capped at 1 req/s per task.
Pricing
Published price — no tokens, no invented credits. A failed task is never charged.
Errors
| HTTP | Code | Meaning |
|---|---|---|
401 | unauthorized | Missing or invalid API key. |
402 | insufficient_balance | Your balance doesn't cover the task price. |
404 | unknown_type | That task type doesn't exist. |
429 | rate_limited | Too many requests. Use the webhook instead of polling. |
Technical notes
What the Jackson-Pollock three-site method measures and what the response contains
This calculator returns the normalized skinfolds and age, the millimetre sum, body_density, body_fat_percent, the method tag jackson_pollock_3site_women, a human-readable formula string, and the precision applied to rounded fields. There is no male coefficient set, no seven-site variant, no ethnicity table, and no population percentile chart in this contract: the engine either computes finite density and fat percent from positive inputs or rejects the request with invalid_input.
How inputs are read, validated, and kept reproducible
Optional leading plus signs and scientific notation on numeric strings are allowed when they parse as finite decimals; embedded spaces, hex prefixes, and non-numeric tokens are rejected with a clear message so a bad cell does not become a wrong fat percentage. Computation multiplies the published coefficients, forms density, then applies Siri without Monte Carlo sampling, external tables, or network I/O. The preferred fields are triceps, suprailiac, and thigh for millimetre skinfolds, and age for years, with aliases triceps_mm and tri; suprailiac_mm, supra, and iliac; thigh_mm and front_thigh; and age_years or years for age. Every required field must be strictly positive: zero, negative, missing, empty, or non-finite values fail with invalid_input and a message that names the offending field and the positivity rule. An optional precision field, with aliases decimals and dp, chooses how many decimal places to expose for the numeric outputs, defaulting to four and capped at fifteen so JSON goldens stay stable; body density is reported with at least six decimal places when precision is lower so the Siri conversion remains auditable. Pair the free browser run on this page with the priced API when you need the identical mathematical result inside an automated pipeline without re-implementing Jackson-Pollock coefficients yourself.
Where female three-site body fat estimates fit in practice and software
On this page the work runs entirely in your browser; through the API each successful lookup costs $0.002, failed validation is not charged, and nothing is stored after the response returns. That split—free interactive exploration and a priced, identical API—matches the rest of the KIT tier-A catalog and lets you move from a classroom demo to an automated pipeline without changing the mathematical result.
Integration use cases
Deterministic health fixtures
Generate reproducible body_density and body_fat_percent fields for unit tests, dashboards, and CI assertions on fixed skinfold inputs.