ForHosting KIT · Developer Utilities

Body fat calculator

Estimates body-fat percentage with the US Navy circumference formula from sex, height_cm, neck_cm and waist_cm (hip_cm required for women), returning the rounded percent and a fitness category.

● BetaFree · in your browser

Run — free How it works & API

Use it from WebAPIEmailTelegramApp soon

How to use it

Enter your values in the form above. The tool checks them before calculating and shows the result on the same page.

Check your inputs

Use the labels and units shown next to each field. If something is missing or outside the allowed range, the page points to the field to fix.

Use it again or automate it

Use the browser tool for individual checks and the API when you need the same capability in an automated workflow.

What you can do with it

Get an answer now

Enter one set of values and see the result without building a spreadsheet or script.

Compare scenarios

Change one value at a time and rerun the calculation to understand what affects the result.

Automate repeated work

Use the API when the same calculation needs to run inside your product or workflow.

FAQ

Which formula is used?

The US Navy circumference method, with separate equations for men and women; method in the output is always us_navy.

Do I need a hip measurement?

Only for women. hip_cm is required when sex is female and ignored for men.

What units are expected?

Centimetres for every measurement. All log10 terms assume cm.

How is the category decided?

The rounded percent is bucketed into essential, athletes, fitness, average or obese using sex-specific thresholds.

Is it medically accurate?

It is a validated estimate, not a clinical measurement like DEXA. Free in the browser; API from $0.002.

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

POSThttps://api.kit.forhosting.com/dev/body-fat

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/dev/body-fat \
  -H "Authorization: Bearer $KIT_KEY" \
  -H "Content-Type: application/json" \
  -d '{"sex":"male","height_cm":180,"neck_cm":38,"waist_cm":85}'

const res = await fetch("https://api.kit.forhosting.com/dev/body-fat", {
  method: "POST",
  headers: {
    "Authorization": `Bearer ${process.env.KIT_KEY}`,
    "Content-Type": "application/json"
  },
  body: JSON.stringify({
    "sex": "male",
    "height_cm": 180,
    "neck_cm": 38,
    "waist_cm": 85
  })
});
const { task_id } = await res.json();

import os, requests

res = requests.post(
    "https://api.kit.forhosting.com/dev/body-fat",
    headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
    json={
    "sex": "male",
    "height_cm": 180,
    "neck_cm": 38,
    "waist_cm": 85
},
)
task_id = res.json()["task_id"]

<?php
$res = file_get_contents("https://api.kit.forhosting.com/dev/body-fat", false, stream_context_create([
  "http" => [
    "method"  => "POST",
    "header"  => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
    "content" => '{"sex":"male","height_cm":180,"neck_cm":38,"waist_cm":85}',
  ],
]));
$task = json_decode($res, true);

body := bytes.NewBufferString(`{"sex":"male","height_cm":180,"neck_cm":38,"waist_cm":85}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/dev/body-fat", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)

Example request

{
  "sex": "male",
  "height_cm": 180,
  "neck_cm": 38,
  "waist_cm": 85
}

Example response

{
  "task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
  "type": "dev.body_fat",
  "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

Per request$0.002

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.

Read the full KIT documentation →

Run — free