ForHosting KIT · Unit converters

Gemstone carat & point converter

One metric carat is exactly 100 points or 0.2 grams, and this converter moves a stone's weight between carats, points, grams, grains and milligrams in any direction. Read a certificate, an invoice or an old grain-based stock card in the unit you need. Free in your browser.

Free
Runs in your browser
No sign-up
Your data stays on your device

Run — free How it works & API

Use it from WebAPIEmailTelegramApp soon

Worked example

If you enter

Value: 1
From: Ct
To: Pt

You get

Result: 100
From label: carat
To label: point
Grams: 0.2

A gemstone carat and point converter turns a stone weight written in metric carats, points, grams, grains, or milligrams into any other unit in that jewelry set without hunting conversion tables or rewriting spreadsheet formulas.

Supported gemstone units and how conversion is computed

The converter accepts five mass families under stable canonical codes: ct for the metric carat, pt for the jewelry point, g for the SI gram, gr for the international grain, and mg for the milligram. Factors follow the international metric carat definition and the conventional point: one carat is exactly two-tenths of a gram (two hundred milligrams), one point is exactly one-hundredth of a carat (two milligrams), one milligram is exactly one thousandth of a gram, and one international grain is sixty-four point seven nine eight nine one milligrams.

Because the intermediate is always grams, converting A to B and B to A is consistent up to the published rounding of twelve decimal places, and there is no pairwise matrix that can drift out of sync. Gold karat purity, troy ounces, pennyweights, and force units are intentionally out of scope so jewelers and gem labs get predictable mass-only results under one clear convention used on diamond certificates, colored-stone invoices, and bench balances.

Quick weight checks for jewelers and gem labs

Use the free in-browser gemstone carat and point converter when you need a quick carats-to-points, points-to-milligrams, or carats-to-grams check while reading a GIA-style certificate, a colored-stone invoice, a bench recipe, or an older grain-based stock card. Open the page, enter the number and units, and copy the result without installing a spreadsheet, a unit library, or a desktop calculator pack. Source inputs follow the same retention rules as other KIT parse items, and results are safe to cache because the algorithm is fully deterministic.

Authors shipping mobile apps or chatbots can map the result, carats, and formula fields directly into cards that show both the number and the conversion path jewelers expect on paper certificates.

What you can do with it

Diamond and gem certificates

Convert carats to points or milligrams so certificate footnotes, lab scales, and retail tags share one mass view without hand-written factors.

Jewelry inventory and wholesale

Normalize carats, points, and grams on invoices, listings, and stock ledgers when suppliers mix metric carats with SI mass.

FAQ

Which units does the gemstone weight converter support?

Metric carats (ct), points (pt), grams (g), grains (gr), and milligrams (mg).

How many points is one carat?

Exactly 100 points. One point is 0.01 carat (2 mg).

How many grams is one carat?

Exactly 0.2 g (200 mg) under the international metric carat.

What happens if I send an unknown unit?

The message names the field and lists supported units. Validation failures are not charged.

Is the gemstone carat converter free?

The browser tool runs free on your device.

Related tools

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/conv/gem-weight

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/conv/gem-weight \
  -H "Authorization: Bearer $KIT_KEY" \
  -H "Content-Type: application/json" \
  -d '{"value":1,"from":"ct","to":"pt"}'

const res = await fetch("https://api.kit.forhosting.com/conv/gem-weight", {
  method: "POST",
  headers: {
    "Authorization": `Bearer ${process.env.KIT_KEY}`,
    "Content-Type": "application/json"
  },
  body: JSON.stringify({
    "value": 1,
    "from": "ct",
    "to": "pt"
  })
});
const { task_id } = await res.json();

import os, requests

res = requests.post(
    "https://api.kit.forhosting.com/conv/gem-weight",
    headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
    json={
    "value": 1,
    "from": "ct",
    "to": "pt"
},
)
task_id = res.json()["task_id"]

<?php
$res = file_get_contents("https://api.kit.forhosting.com/conv/gem-weight", false, stream_context_create([
  "http" => [
    "method"  => "POST",
    "header"  => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
    "content" => '{"value":1,"from":"ct","to":"pt"}',
  ],
]));
$task = json_decode($res, true);

body := bytes.NewBufferString(`{"value":1,"from":"ct","to":"pt"}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/conv/gem-weight", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)

Example request

{
  "value": 1,
  "from": "ct",
  "to": "pt"
}

Example response

{
  "task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
  "type": "conv.gem_weight",
  "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.

Technical notes

The browser tool runs free on your device; the prepaid API charges $0.002 per successful item when pipelines need the same contract from servers and automation.

Supported gemstone units and how conversion is computed

Friendly aliases such as carat, carats, metric carat, point, points, gram, grams, grain, grains, milligram, and milligrams are normalized case-insensitively so forms and APIs can pass either short codes or full names. Every request multiplies the input value by the exact grams-per-unit factor for the source, then divides by the grams-per-unit factor for the target.

Request shape, response fields, and unknown-unit errors

The error message names the bad field and lists the supported set so clients can correct forms without guessing. Zero converts cleanly to zero in every target unit; negative values are allowed when you need signed weight deltas in inventory pipelines. Send a JSON body with three required fields: value as a finite number, from as the source unit string, and to as the target unit string. Aliases amount, quantity, and weight are accepted for value; unit_from and source for from; unit_to and target for to. On success the response echoes the canonical from and to codes, human-readable from_label and to_label strings, the converted result, the intermediate grams quantity, an intermediate carats quantity for jewelry display, the dimensionless factor from source to target, a short formula line suitable for UI display, the method tag gem_weight_si, and the fixed list of units_supported. Missing value, non-finite numbers such as NaN or Infinity, missing unit fields, and any token that does not map to a supported unit fail with invalid_input and are not charged after the engine rejects the request. Identical inputs always yield identical JSON because the path is pure arithmetic with no randomness, no remote lookup, and no dependence on the wall clock, which makes the endpoint safe to pin in continuous-integration goldens and SDK contract tests. Point-scale melee and multi-carat center stones share the same code path, so extreme magnitude pairs remain well-defined as long as IEEE double precision can represent the intermediate grams product.

Browser use, API pricing, and jewelry or lab workflows

Switch to the prepaid API when a jewelry inventory system, e-commerce listing tool, diamond wholesale platform, gemological notebook, or materials pipeline must convert carat-scale and gram-scale weights at scale under a stable KIT contract at $0.002 per successful item; validation failures that raise invalid_input do not consume balance after rejection. Pair this endpoint with length or volume converters when a product pipeline needs several measure families, or call it alone when search traffic is specifically for gemstone carat and point conversion rather than a general unit switchboard.

Integration use cases

Apps and automated pipelines

Call a prepaid, deterministic gemstone weight API from inventory tools and e-commerce with clear invalid_input on unknown units.

Read the full KIT documentation →

Run — free

Worked example

Supported gemstone units and how conversion is computed

Quick weight checks for jewelers and gem labs

What you can do with it

Diamond and gem certificates

Jewelry inventory and wholesale

FAQ

Related tools

For developers — API access

API endpoint

Call it from your stack

Example request

Example response

Pricing

Errors

Technical notes

Supported gemstone units and how conversion is computed

Request shape, response fields, and unknown-unit errors

Browser use, API pricing, and jewelry or lab workflows

Integration use cases

Apps and automated pipelines

thank you