ForHosting KIT · Developer Utilities

Percent to molarity calculator

This percent-to-molarity calculator converts a solution’s mass percent by weight, its density, and the solute’s molar mass into molarity in moles per litre.

● BetaFree · in your browser

Run — free How it works & API

Use it from WebAPIEmailTelegramApp soon

Reagent bottles and many lab protocols still list concentration as a weight percent with a table density, while stoichiometry, titrations, and rate laws almost always need moles per litre. The conversion used here is fully deterministic: molarity equals mass percent times density times ten, divided by molar mass, when density is in grams per millilitre and molar mass is in grams per mole. Classic checks include about thirty-seven percent hydrochloric acid near density one point one nine with molar mass thirty-six point four six yielding roughly twelve molar, and ten percent sodium hydroxide at density one point one one with molar mass forty yielding two point seven seven five molar. 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, stock-solution prep, and bottle-label conversions, or call the API at $0.002 per successful request when you need reproducible molarity fixtures in CI, tutoring software, or teaching demos.

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/chem/percent-to-molarity

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/chem/percent-to-molarity \
  -H "Authorization: Bearer $KIT_KEY" \
  -H "Content-Type: application/json" \
  -d '{"mass_percent":37,"density":1.19,"molar_mass":36.46}'

const res = await fetch("https://api.kit.forhosting.com/chem/percent-to-molarity", {
  method: "POST",
  headers: {
    "Authorization": `Bearer ${process.env.KIT_KEY}`,
    "Content-Type": "application/json"
  },
  body: JSON.stringify({
    "mass_percent": 37,
    "density": 1.19,
    "molar_mass": 36.46
  })
});
const { task_id } = await res.json();

import os, requests

res = requests.post(
    "https://api.kit.forhosting.com/chem/percent-to-molarity",
    headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
    json={
    "mass_percent": 37,
    "density": 1.19,
    "molar_mass": 36.46
},
)
task_id = res.json()["task_id"]

<?php
$res = file_get_contents("https://api.kit.forhosting.com/chem/percent-to-molarity", false, stream_context_create([
  "http" => [
    "method"  => "POST",
    "header"  => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
    "content" => '{"mass_percent":37,"density":1.19,"molar_mass":36.46}',
  ],
]));
$task = json_decode($res, true);

body := bytes.NewBufferString(`{"mass_percent":37,"density":1.19,"molar_mass":36.46}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/chem/percent-to-molarity", 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_percent": 37,
  "density": 1.19,
  "molar_mass": 36.46
}

Example response

{
  "task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
  "type": "chem.percent_to_molarity",
  "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_value 1000000000000000

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