Molar mass converter
Convert molar mass between g/mol, kg/mol and kg/kmol: water's 18.015 g/mol is also 18.015 kg/kmol, while 1 kg/mol is 1000 g/mol. Keeps lab sheets and process data in one unit. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Value
- 18.015
- Source unit
- g/mol
- Target unit
- kg/kmol
- Result
- 18.015
- From label
- grams per mole
- To label
- kilograms per kilomole
- G per mol
- 18.015
A molar mass converter turns a quantity written in one molar-mass unit into another without hunting SI-prefix tables or rewriting spreadsheet formulas.
Supported units and how the conversion is computed
The converter accepts three molar-mass families under stable canonical codes: g/mol for grams per mole, kg/mol for kilograms per mole, and kg/kmol for kilograms per kilomole. Factors follow SI prefix arithmetic: one gram per mole is one gram per mole, one kilogram per mole is one thousand grams per mole, and one kilogram per kilomole equals one gram per mole because one kilogram over one thousand moles reduces to one gram per mole.
That identity is the classic classroom fact that water near eighteen point zero one five grams per mole is also eighteen point zero one five kilograms per kilomole. Because the intermediate is always grams per mole, 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.
Formula-to-mass calculation is intentionally out of scope so this landing stays a pure unit converter; use a dedicated molar-mass calculator when you need atomic weights from a chemical formula.
Who uses molar mass unit conversion
Use the free in-browser molar mass converter when you need a quick grams-per-mole to kilograms-per-kilomole or kilograms-per-mole check while reading a lab procedure, process datasheet, thermodynamics table, or homework problem. 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 and formula fields directly into cards that show both the number and the conversion path students and engineers expect on paper.
What you can do with it
Classroom SI-prefix drills
Convert water or oxygen molar mass between g/mol and kg/kmol so students see that the numbers match under SI prefixes without memorizing a separate table.
Process engineering data sheets
Normalize kg/mol and g/mol labels from mixed vendor PDFs into one unit before feeding flowsheet or reactor models.
FAQ
Which molar mass units does this converter support?
Grams per mole (g/mol), kilograms per mole (kg/mol), and kilograms per kilomole (kg/kmol).
Is 1 g/mol the same as 1 kg/kmol?
Yes. Under SI prefixes, one kilogram per kilomole equals one gram per mole, so those two units are numerically identical. One kilogram per mole equals one thousand grams per mole.
What happens if I send an unknown unit?
The message names the field and lists supported units. Validation failures are not charged.
Is the molar mass converter free?
The browser tool runs free on your device.
Can it work out molar mass from a chemical formula?
No. It only converts a molar mass you already have from one unit to another. To get the value from the atomic weights in a formula, use a dedicated molar mass calculator.
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/molar-mass \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"value":18.015,"from":"g/mol","to":"kg/kmol"}'const res = await fetch("https://api.kit.forhosting.com/conv/molar-mass", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"value": 18.015,
"from": "g/mol",
"to": "kg/kmol"
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/conv/molar-mass",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"value": 18.015,
"from": "g/mol",
"to": "kg/kmol"
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/conv/molar-mass", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"value":18.015,"from":"g/mol","to":"kg/kmol"}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"value":18.015,"from":"g/mol","to":"kg/kmol"}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/conv/molar-mass", 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": 18.015,
"from": "g/mol",
"to": "kg/kmol"
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "conv.molar_mass",
"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
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 units and how the conversion is computed
Friendly aliases such as grams per mole, kilograms per mole, kilograms per kilomole, g per mol, kg per kmol, and reciprocal forms like g·mol-1 or kg·kmol-1 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-mole factor for the source, then divides by the grams-per-mole 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. Negative values are allowed when you need signed molar-mass deltas in engineering pipelines; zero converts cleanly to zero in every target unit. 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 mass 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 g_per_mol quantity, the dimensionless factor from source to target, a short formula line suitable for UI display, the method tag molar_mass_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. Water-scale results near eighteen grams per mole and polymer-scale results near hundreds of kilograms per mole share the same code path, so magnitude pairs remain well-defined as long as IEEE double precision can represent the intermediate product.
Browser use, API pricing, and everyday workflows
Switch to the prepaid API when a chemistry homework checker, process-engineering calculator, materials LIMS, polymer characterization pipeline, or educational chatbot must convert molar mass 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 a formula-based molar mass calculator when search traffic starts from a chemical formula rather than a unit swap, or call it alone when the query is specifically for unit conversion among g/mol, kg/mol, and kg/kmol.
Integration use cases
Lab LIMS and homework APIs
Accept student or instrument unit strings, return a deterministic converted molar mass, and raise invalid_input on unknown tokens under a prepaid KIT contract.
Technical questions
How do I convert 18.015 g/mol to kg/kmol?
Send JSON with value: 18.015, from: "g/mol", to: "kg/kmol". The response result field is 18.015, plus a g_per_mol intermediate and a readable formula.