ForHosting KIT · Developer Utilities

Vital capacity calculator

Vital capacity is the largest volume of air a person can exhale after a full inhalation.

● BetaFree · in your browser

Use it from WebAPIEmailTelegramApp soon

Predicted vital capacity is the reference value expected for a healthy adult of a given standing height, chronological age, and biological sex. This calculator applies the Baldwin, Cournand, and Richards equations, the classic linear reference formulas used in physiology teaching to estimate that volume in liters. Enter height in centimeters, age in years, and sex; the solver returns the predicted capacity together with the formula that produced it. Height and age must be finite positive numbers. The same pure arithmetic powers the free browser widget and the API, so classroom keys and automation scripts never disagree. Successful API calls cost $0.002 per item; failed validation is not charged. Results are educational estimates, not a clinical diagnosis or a substitute for laboratory spirometry performed by a qualified professional.

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 vital capacity 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.

How is predicted vital capacity calculated?

The Baldwin-Cournand-Richards equations estimate VC in liters from height in centimeters, age in years, and sex. Males: (27.63 − 0.112 × age) × height_cm / 1000. Females: (21.78 − 0.101 × age) × height_cm / 1000. Example: 175 cm, 30 years, male yields 4.24725 L.

What happens if height or age is zero or negative?

The input is rejected with invalid_input. Height and age must be positive numbers because the reference equations are undefined for non-positive stature or age.

Is predicted vital capacity a clinical diagnosis?

No. The result is an educational reference estimate from published equations. It does not interpret a measured spirogram, compute percent of predicted from a real FVC, or replace a pulmonary-function laboratory.

Which units does the calculator use?

Height is standing centimeters, age is years, and predicted vital capacity is returned in liters under predicted_vc_l with unit L. Convert inches to centimeters before sending height.

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/vital-capacity

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/vital-capacity \
  -H "Authorization: Bearer $KIT_KEY" \
  -H "Content-Type: application/json" \
  -d '{"height":175,"age":30,"sex":"male"}'

const res = await fetch("https://api.kit.forhosting.com/health/vital-capacity", {
  method: "POST",
  headers: {
    "Authorization": `Bearer ${process.env.KIT_KEY}`,
    "Content-Type": "application/json"
  },
  body: JSON.stringify({
    "height": 175,
    "age": 30,
    "sex": "male"
  })
});
const { task_id } = await res.json();

import os, requests

res = requests.post(
    "https://api.kit.forhosting.com/health/vital-capacity",
    headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
    json={
    "height": 175,
    "age": 30,
    "sex": "male"
},
)
task_id = res.json()["task_id"]

<?php
$res = file_get_contents("https://api.kit.forhosting.com/health/vital-capacity", false, stream_context_create([
  "http" => [
    "method"  => "POST",
    "header"  => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
    "content" => '{"height":175,"age":30,"sex":"male"}',
  ],
]));
$task = json_decode($res, true);

body := bytes.NewBufferString(`{"height":175,"age":30,"sex":"male"}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/health/vital-capacity", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)

Example request

{
  "height": 175,
  "age": 30,
  "sex": "male"
}

Example response

{
  "task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
  "type": "health.vital_capacity",
  "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.

Limits

`max_height_cm`	250
`max_age_years`	120

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 →