Grams to carats converter
One gram is exactly 5 metric carats, because the carat has been fixed at 0.2 grams since 1907. Turn a balance reading in grams into the carat weight that gem certificates, invoices and shop tags use. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Grams
- 0.2
- Result
- 1 ct
- Converted
- 1
- Carats
- 1
- From unit
- g
A grams-to-carats converter turns a metric mass reading into the gemology carat value used on diamond certificates, jewellery invoices, and classroom worksheets. Approximate mental shortcuts such as “about five times” without stating the 0.2 gram definition are unnecessary: the path hard-codes carats equals grams times five so lab notes and homework checks match engineering tables.
Why grams and metric carats meet at exactly 0.2 g
Grams belong to the SI mass family used on laboratory balances, shipping manifests, and most product labels worldwide. The metric carat remains the familiar unit for gemstone mass in the jewellery trade: diamonds, sapphires, rubies, and other precious stones are quoted in carats on certificates and retail tags rather than grams. The bridge is exact by international definition, not a survey approximation.
Since the 1907 adoption of the metric carat, one carat has been fixed at exactly two hundred milligrams—zero point two grams—with no leftover uncertainty. That makes the conversion a single exact multiplication: carats equals grams times five, or equivalently grams divided by zero point two. Rough rules of thumb that round intermediate values introduce scale error that shows up on a one-carat stone or a multi-carat parcel.
Do not confuse this mass carat with gold karat purity, which measures alloy fineness on a twenty-four-part scale and is a different search intent entirely.
Practical tips, checks, and related searches
Prefer sending bare numbers when you control the client; string numbers are accepted only when they match a strict finite numeric pattern without units, thousand separators, or currency symbols. Round-trip sanity checks are easy: convert the textbook value zero point two grams and confirm you receive exactly one carat after rounding, or convert one gram and confirm exactly five carats.
When teaching, pair the exact path with a rough mental shortcut so students see that five times works because the definition is zero point two grams, not because of a coincidence. Stay inside the absolute range so the multiplication cannot overflow into a non-finite result the solver must reject.
This landing targets people searching for grams to carats, convert grams to carats, or an exact zero point two metric carat calculator; it is not a gold karat purity tool, not a carats-to-grams primary form, not a multi-unit mass hub, and not a troy-ounce converter. Prefer this capability when the input is already in grams and you only need carats for gemology or jewellery work; if you must convert among many mass units in one call, use a broader unit converter instead.
What you can do with it
Diamond and gemstone certificates
Turn laboratory gram readings into metric carats for certificate fields, inventory systems, and retail tags with the same exact 0.2 g factor every row.
Jewellery workshop weighing
Bench jewellers convert gram scale readouts to carats for parcels, melee lots, and custom pieces before quoting customers.
FAQ
What formula converts grams to carats?
Carats = grams × 5. One metric carat is exactly 0.2 grams (200 mg), so one gram equals exactly five carats.
Is 0.2 g per carat exact or approximate?
Exact. The metric carat has been fixed at 200 milligrams (0.2 g) since the 1907 international adoption. This tool multiplies by five; it does not use rough estimates.
Is this the same as gold karat?
No. Gold karat measures alloy purity on a 24-part scale. This capability converts mass grams to gemology carats (ct). Use a gold karat converter for fineness.
Is the grams to carats converter free?
The browser tool is free and runs locally.
How do I convert carats back to grams?
Divide the carats by 5, or multiply them by 0.2. A 5-carat parcel therefore weighs exactly 1 gram, and a 1-carat stone weighs 0.2 grams, which is 200 milligrams.
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
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/grams-to-carats \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"grams":0.2}'const res = await fetch("https://api.kit.forhosting.com/conv/grams-to-carats", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"grams": 0.2
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/conv/grams-to-carats",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"grams": 0.2
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/conv/grams-to-carats", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"grams":0.2}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"grams":0.2}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/conv/grams-to-carats", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"grams": 0.2
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "conv.grams_to_carats",
"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
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
Invalid or missing input fails with a clear invalid_input error instead of inventing a number.
How to call the API and what comes back
Absolute values must stay within the published limit of one trillion. Use this path when the input is already in grams and you only need metric carats; for gold purity or multi-unit mass hubs, choose a different capability. Send a JSON body with one required finite number field named grams. Aliases g, gram, value, mass, weight, and grams_value are accepted so SDK clients and form posts can use the name that fits the product. On success the response echoes rounded grams, sets carats, result, and converted to the same rounded carat magnitude, unit to the token ct, from_unit to g and to_unit to ct, factor to five, grams_per_carat to zero point two, carats_per_gram to five, formula to the string carats equals grams times five, message to a short English summary, and steps to an ordered array of substitution lines that show the metric-carat definition. Failed validation—missing fields, non-finite numbers, bare plus or minus signs, non-numeric strings, values outside absolute limits, or a non-finite converted result—returns invalid_input and is never charged. Pricing is a flat $0.002 per successful request with unit item.
Practical tips, checks, and related searches
Failed tasks that return invalid_input do not consume prepaid balance, which keeps exploratory scripts cheap when learners deliberately omit grams or pass text.
Integration use cases
Homework and unit-test fixtures
Students and engineers convert classroom gram masses to carats and pin golden JSON so browser and API arithmetic never drift.
Technical questions
What happens on missing or non-numeric input?
The API returns invalid_input naming the problem (for example a missing grams field). Failed tasks are not charged.