Molar concentration calculator
Half a mole of solute in 2 L of solution is 0.25 mol/L. Enter moles and volume, or a weighed mass with its molar mass, and get the molarity of the solution you made up. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Moles
- 0.5
- Solution volume in litres
- 2
- Concentration
- 0.25
- Solute source
- moles
- Precision
- 10
This molar concentration calculator finds the molarity of a solution when you know how much solute is present and the total solution volume in litres. Molar concentration, often written c or M and reported in moles per litre, is defined by the simple ratio c equals n over V, where n is the amount of solute in moles and V is the volume of the solution. When you already know the mole amount, enter moles and volume; when you have a weighed sample instead, enter mass and molar mass so the engine first forms n equals mass over molar mass, then divides by volume. Common classroom checks include half a mole in two litres yielding one quarter mole per litre, and fifty-eight point four four grams of a substance with molar mass fifty-eight point four four grams per mole dissolved to one litre yielding one mole per litre. The engine uses only finite deterministic arithmetic with no network calls, no sampling, and no date-dependent shortcuts.
What molar concentration means and what you get
Molar concentration, also called molarity, measures how much solute is present per unit volume of solution. In the standard SI-friendly definition used in general chemistry, c equals n divided by V, with n in moles and V in litres, so the unit is moles per litre, often abbreviated mol per L or M. That definition is a state of the prepared solution, not a property of the pure solute alone: the same mass of solid can produce different molarities if it is dissolved to different final volumes.
Amount of solute may be known directly as moles, or derived from a weighed mass using the molar mass of the compound via n equals mass over molar mass, which is the usual path when a bottle lists only grams and a molecular weight. Volume here is the total volume of the solution after mixing, not the volume of solvent poured alone, which is the distinction students must keep when a protocol says dilute to the mark. Zero moles with a positive volume is valid and yields zero concentration.
Where molar concentration fits in study, lab work, and software
Students meet c equals n over V when a textbook introduces solution concentration, when a homework problem gives grams and molar mass and asks for molarity, or when a contest problem supplies moles and litres and expects moles per litre without a calculator that silently changes units. Teachers can pre-generate answer keys for stock solutions and dilution setups without trusting opaque apps that confuse mass percent with molarity or assume millilitres when the statement says litres.
Lab technicians and preparers use the same definition when a protocol requires a stated molarity and only a balance and volumetric flask are available: convert mass to moles with the molar mass, divide by the flask volume in litres, and confirm the target concentration. Developers call the same contract from scripts to seed deterministic test vectors for chemistry tutors, to normalize user-entered solution parameters before a lab notebook export, or to satisfy programming-challenge statements that demand mol per L rather than a hand-waved sketch.
What you can do with it
Homework and lab checks
Compute c = n/V from moles or from mass and molar mass before grading worksheets or preparing stock solutions.
Tutoring and teaching software
Normalize user-entered solute amount and volume into molarity for interactive lessons and step helpers.
FAQ
What does the molar concentration calculator cost?
It is free in your browser on this page.
How is molar concentration defined?
c = n / V, with n in moles of solute and V in litres of solution. The result is in mol/L (molarity).
What happens if volume is zero or negative?
Non-positive volume makes c = n/V undefined or non-physical.
Does this convert millilitres to litres?
No. Enter volume already in litres (for example 250 mL as 0.25 L). The engine does not convert volume units.
Can I enter grams instead of moles?
Yes. Leave the moles empty and give the mass and the molar mass instead; the calculator divides one by the other first. For example, 58.44 g of a substance at 58.44 g/mol made up to 1 L is 1 mol/L.
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/chem/molar-concentration \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"volume":2,"moles":0.5}'const res = await fetch("https://api.kit.forhosting.com/chem/molar-concentration", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"volume": 2,
"moles": 0.5
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/chem/molar-concentration",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"volume": 2,
"moles": 0.5
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/chem/molar-concentration", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"volume":2,"moles":0.5}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"volume":2,"moles":0.5}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/chem/molar-concentration", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"volume": 2,
"moles": 0.5
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "chem.molar_concentration",
"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.
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. |
Technical notes
What molar concentration means and what the response contains
This calculator returns the resolved moles, optional mass and molar mass when they were used or supplied, the volume, the computed concentration, a solute_source tag indicating whether moles were given or derived from mass, the precision used, a method tag molar_concentration, a short formula reminder, and a unit hint mol/L. There is no unit conversion from millilitres to litres, no density-based mass-percent path, and no activity-coefficient correction: the engine either evaluates c equals n over V inside the supported numeric range or rejects the input with invalid_input. Rejected cases include a missing volume, non-finite values, magnitudes above the documented ceiling, any volume that is zero or negative because division by a non-positive volume is undefined or non-physical, negative moles or mass, and a missing solute description when neither moles nor the mass-plus-molar-mass pair is provided.
How moles, mass, molar mass, and volume are read and stay reproducible
Mass and moles must be non-negative; molar mass must be strictly positive so that n equals mass over molar mass is defined. Optional leading plus signs and scientific notation on numeric strings are allowed when they parse as finite decimals; embedded spaces and non-numeric tokens are rejected. The preferred field for amount of solute in moles is moles, but aliases n, mol, amount, and amount_mol are accepted so spreadsheets, query strings, and typed forms can reuse the same contract. When moles is omitted, both mass and molar_mass must be present: mass has aliases m, mass_g, grams, and weight, and molar_mass has aliases M, mm, molecular_weight, mw, and molarMass. The preferred field for solution volume is volume, with aliases V, v, liters, litres, and volume_L. Volume must be a finite positive number of litres: zero or negative values fail with invalid_input and a message that names the field and explains that molar concentration c equals n over V is undefined or non-physical for non-positive volume, so a bad cell does not become a silent infinity or nonsense result. An optional precision field, with aliases decimals and dp, chooses how many decimal places to expose for the numeric outputs, defaulting to ten and capped at fifteen so JSON goldens stay stable. Pair the free browser run on this page with the priced API when you need the identical mathematical result inside an automated pipeline without re-implementing the molar concentration formula yourself.
Where molar concentration fits in study, lab work, and software
Product and education tools use the endpoint when a learner types amount and volume and the UI must show molar concentration with a clear unit. On this page the work runs entirely in your browser; through the API each successful lookup costs $0.002, failed validation is not charged, and nothing is stored after the response returns. That split — free interactive exploration and a priced, identical API — matches the rest of the KIT tier-A catalog and lets you move from a classroom demo to an automated pipeline without changing the mathematical result. Pair it with dilution or stoichiometry helpers when you need related solution quantities, and with other science endpoints when you are building a small lab of free, deterministic chemistry calculators.
Integration use cases
Deterministic test fixtures
Generate reproducible molar concentration values for unit tests, chemistry tutors, and CI assertions on c = n/V.
Technical questions
What if I only know mass, not moles?
Provide mass and molar_mass instead of moles. The calculator uses n = mass / molar_mass, then c = n / V.