ForHosting KIT · Developer Utilities

Frequency to note calculator

This frequency to note calculator turns a tone measured in hertz into the nearest equal-temperament musical note, its scientific octave, and the cents offset from that pitch under a chosen concert reference for A4.

● BetaFree · in your browser

Run — free How it works & API

Use it from WebAPIEmailTelegramApp soon

Musicians, audio engineers, instrument builders, and teachers often know a measured frequency from a tuner, spectrum analyzer, or physics lab but need the closest named pitch and how far it sits from perfect intonation. The mapping is fully deterministic twelve-tone equal temperament: continuous MIDI equals sixty-nine plus twelve times the base-two log of frequency over A4, the nearest note is the rounded MIDI integer, and cents equal one hundred times the fractional remainder. Concert A at four hundred forty hertz lands on A4 with zero cents; middle C near two hundred sixty-one point six hertz lands on C4; a slightly sharp four hundred forty-five hertz reports A4 a few cents above the reference. The engine uses only finite arithmetic with no network calls, no sampling, and no date-dependent shortcuts. Use it free in the browser for tuning checks, ear-training demos, and homework, or call the API at $0.002 per successful request when you need reproducible note labels and cents in CI, DAW helpers, 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/hobby/frequency-to-note

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/hobby/frequency-to-note \
  -H "Authorization: Bearer $KIT_KEY" \
  -H "Content-Type: application/json" \
  -d '{"frequency":440}'

const res = await fetch("https://api.kit.forhosting.com/hobby/frequency-to-note", {
  method: "POST",
  headers: {
    "Authorization": `Bearer ${process.env.KIT_KEY}`,
    "Content-Type": "application/json"
  },
  body: JSON.stringify({
    "frequency": 440
  })
});
const { task_id } = await res.json();

import os, requests

res = requests.post(
    "https://api.kit.forhosting.com/hobby/frequency-to-note",
    headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
    json={
    "frequency": 440
},
)
task_id = res.json()["task_id"]

<?php
$res = file_get_contents("https://api.kit.forhosting.com/hobby/frequency-to-note", false, stream_context_create([
  "http" => [
    "method"  => "POST",
    "header"  => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
    "content" => '{"frequency":440}',
  ],
]));
$task = json_decode($res, true);

body := bytes.NewBufferString(`{"frequency":440}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/hobby/frequency-to-note", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)

Example request

{
  "frequency": 440
}

Example response

{
  "task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
  "type": "hobby.frequency_to_note",
  "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