ForHosting KIT · Developer Utilities

Planet density calculator

This planet density calculator returns the mean bulk density of a planet, moon, dwarf planet, or star from its total mass and mean radius under the uniform-sphere model.

● BetaFree · in your browser

Run — free How it works & API

Use it from WebAPIEmailTelegramApp soon

The closed form is fully deterministic: density equals three times mass over four pi times radius cubed, which is the same as mass divided by the sphere volume four-thirds pi R cubed. With SI inputs — mass in kilograms and radius in metres — the result is in kilograms per cubic metre, the unit textbooks and planetary data tables use for bulk density comparisons. A well-known check is Earth-scale mass 5.972 times ten to the twenty-four kilograms and mean radius 6.371 times ten to the six metres, which yields about 5514 kilograms per cubic metre. The engine uses only finite arithmetic with no network calls, no sampling, and no date-dependent shortcuts. Use it free in the browser for homework, exoplanet comparison, and contest drills, or call the API at $0.002 per successful request when you need reproducible density fixtures in CI, astronomy demos, or teaching software.

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

How do I use this capability?

Complete the fields above and run it on this page. The form highlights anything that needs attention.

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/astro/planet-density

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/astro/planet-density \
  -H "Authorization: Bearer $KIT_KEY" \
  -H "Content-Type: application/json" \
  -d '{"mass":5.972e+24,"radius":6371000}'

const res = await fetch("https://api.kit.forhosting.com/astro/planet-density", {
  method: "POST",
  headers: {
    "Authorization": `Bearer ${process.env.KIT_KEY}`,
    "Content-Type": "application/json"
  },
  body: JSON.stringify({
    "mass": 5.972e+24,
    "radius": 6371000
  })
});
const { task_id } = await res.json();

import os, requests

res = requests.post(
    "https://api.kit.forhosting.com/astro/planet-density",
    headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
    json={
    "mass": 5.972e+24,
    "radius": 6371000
},
)
task_id = res.json()["task_id"]

<?php
$res = file_get_contents("https://api.kit.forhosting.com/astro/planet-density", false, stream_context_create([
  "http" => [
    "method"  => "POST",
    "header"  => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
    "content" => '{"mass":5.972e+24,"radius":6371000}',
  ],
]));
$task = json_decode($res, true);

body := bytes.NewBufferString(`{"mass":5.972e+24,"radius":6371000}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/astro/planet-density", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)

Example request

{
  "mass": 5.972e+24,
  "radius": 6371000
}

Example response

{
  "task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
  "type": "astro.planet_density",
  "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_abs_mass`	1e+40
`max_abs_radius`	100000000000000000000

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