ForHosting KIT · Developer Utilities

Estimated fetal weight calculator

This estimated fetal weight calculator applies the classic Hadlock four-parameter equation to standard obstetric ultrasound biometry: biparietal diameter, head circumference, abdominal circumference, and femur length.

● BetaFree · in your browser

Run — free How it works & API

Use it from WebAPIEmailTelegramApp soon

The model maps those lengths, expressed in centimetres, through a published log10 polynomial and returns estimated fetal weight in grams, kilograms, and pounds without network calls, sampling, or date-dependent shortcuts. Students, sonography trainees, and software teams use a deterministic Hadlock path when worksheets, LMS items, and CI fixtures must match the same coefficients every time. Enter measurements in centimetres or millimetres, optionally set decimal precision, and read back normalized centimetre values, the intermediate log10 result, a formula string, and step lines you can show beside the answer. The free browser run on this page uses the same pure module as the API, so homework checks and automation never disagree on a borderline biometry set. Failed validation is not billed; each successful API estimate costs $0.002. Treat the output as an educational and engineering estimate, not a clinical diagnosis or substitute for professional obstetric judgment.

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

What does the estimated fetal weight Hadlock calculator cost?

It is free in your browser on this page. Through the API a successful request costs $0.002; invalid inputs are not charged.

Which formula does this tool use?

The four-parameter Hadlock model: log10(EFW in grams) = 1.3596 − 0.00386×AC×FL + 0.0064×HC + 0.00061×BPD×AC + 0.0424×AC + 0.174×FL, with lengths in centimetres.

Which ultrasound measurements are required?

All four: biparietal diameter (bpd), head circumference (hc), abdominal circumference (ac), and femur length (fl). Missing any field fails with invalid_input.

Can I enter millimetres instead of centimetres?

Yes. Set unit to mm (or length_unit / measure_unit). All four lengths share that unit and are converted to centimetres before the formula.

Is this medical advice or a diagnostic tool?

No. The result is an educational and engineering estimate from published coefficients. Clinical decisions need professional obstetric interpretation and institutional protocols.

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/health/efw-hadlock

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/efw-hadlock \
  -H "Authorization: Bearer $KIT_KEY" \
  -H "Content-Type: application/json" \
  -d '{"bpd":9,"hc":32.5,"ac":31,"fl":6.5}'

const res = await fetch("https://api.kit.forhosting.com/health/efw-hadlock", {
  method: "POST",
  headers: {
    "Authorization": `Bearer ${process.env.KIT_KEY}`,
    "Content-Type": "application/json"
  },
  body: JSON.stringify({
    "bpd": 9,
    "hc": 32.5,
    "ac": 31,
    "fl": 6.5
  })
});
const { task_id } = await res.json();

import os, requests

res = requests.post(
    "https://api.kit.forhosting.com/health/efw-hadlock",
    headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
    json={
    "bpd": 9,
    "hc": 32.5,
    "ac": 31,
    "fl": 6.5
},
)
task_id = res.json()["task_id"]

<?php
$res = file_get_contents("https://api.kit.forhosting.com/health/efw-hadlock", false, stream_context_create([
  "http" => [
    "method"  => "POST",
    "header"  => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
    "content" => '{"bpd":9,"hc":32.5,"ac":31,"fl":6.5}',
  ],
]));
$task = json_decode($res, true);

body := bytes.NewBufferString(`{"bpd":9,"hc":32.5,"ac":31,"fl":6.5}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/health/efw-hadlock", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)

Example request

{
  "bpd": 9,
  "hc": 32.5,
  "ac": 31,
  "fl": 6.5
}

Example response

{
  "task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
  "type": "health.efw_hadlock",
  "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 →