Oxygen for combustion calculator
One mole of propane, C3H8, needs 5 moles of oxygen to burn completely and gives 3 moles of carbon dioxide and 4 of water. Enter the moles of fuel and its carbon and hydrogen counts for any CₓHᵧ hydrocarbon. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Moles
- 1
- Carbons
- 3
- Hydrogens
- 8
- O2 per mole fuel
- 5
- Oxygen moles
- 5
- Co2 moles
- 3
- H2o moles
- 4
This oxygen for combustion calculator turns moles of a hydrocarbon fuel and its carbon and hydrogen atom counts into the moles of molecular oxygen required for complete combustion. You supply the moles of fuel, the number of carbon atoms x in CₓHᵧ, and the number of hydrogen atoms y. Classic classroom checks include one mole of propane C₃H₈ needing five moles of O₂, and two moles of methane CH₄ needing four moles of O₂. The engine uses only finite deterministic arithmetic with no network calls, no sampling, and no date-dependent shortcuts.
What the oxygen demand means and what you get
For complete combustion of a hydrocarbon written as CₓHᵧ, every carbon atom becomes one molecule of carbon dioxide and every two hydrogen atoms become one molecule of water, so the oxygen demand is fixed once x, y, and the moles of fuel are known. Balancing the reaction CₓHᵧ plus oxygen going to carbon dioxide and water yields an O₂ coefficient of x plus y over four per mole of fuel.
Multiplying that coefficient by the moles of hydrocarbon produces the moles of O₂ that must be supplied for complete combustion under ideal conditions. Zero moles of fuel with non-negative atom counts is allowed and yields zero oxygen moles, which is the correct ideal limit when no fuel is present. Negative carbon or hydrogen counts are also rejected.
Where oxygen-for-combustion calculation fits in study, lab work, and software
Students meet oxygen-required combustion problems when a textbook introduces hydrocarbon burning after balancing simple equations, when a homework set gives moles of propane or butane and asks for moles of O₂ before any air-volume conversion, or when a contest problem expects a clear oxygen-mole intermediate before discussing excess air. Teachers can pre-generate answer keys for integer formulas such as CH₄, C₂H₆, and C₃H₈ without trusting opaque apps that jump straight to grams of air or mix incomplete combustion with complete-combustion stoichiometry.
Lab technicians and preparers use the same closed form when a protocol already states moles of a pure hydrocarbon fuel and only the atom counts remain: apply x plus y over four and plan how much pure oxygen is ideally required. Developers call the same contract from scripts to seed deterministic test vectors for chemistry tutors, to normalize user-entered fuel parameters before a lab notebook export, or to satisfy programming-challenge statements that demand oxygen moles rather than a hand-waved sketch.
What you can do with it
Homework and combustion checks
Convert moles of CₓHᵧ and atom counts into moles of O₂ required for complete combustion before air-volume or mass steps.
Lab prep and education software
Compute ideal oxygen demand from measured fuel moles in lab notebooks, tutoring UIs, and automated worksheet generators.
FAQ
What does the oxygen for combustion calculator cost?
It is free in your browser on this page.
What happens if moles is negative?
Moles of hydrocarbon fuel cannot be negative for oxygen-required combustion stoichiometry.
Does this tool convert oxygen moles into air volume or fuel mass?
No. It only returns oxygen moles (and related product moles) from fuel moles and C/H counts. Use a gas-volume or mass tool if you need those conversions.
Why are results rounded to a precision?
Default precision is 10 decimal places; you can set precision from 0 to 15.
Where does the rule of carbons plus a quarter of the hydrogens come from?
From balancing complete combustion. Each carbon atom ends up in one carbon dioxide molecule, which takes one O2, and every two hydrogen atoms form one water molecule, which takes half an O2. That adds up to the carbons plus a quarter of the hydrogens per mole of fuel.
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/oxygen-required-combustion \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"moles":1,"carbons":3,"hydrogens":8}'const res = await fetch("https://api.kit.forhosting.com/chem/oxygen-required-combustion", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"moles": 1,
"carbons": 3,
"hydrogens": 8
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/chem/oxygen-required-combustion",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"moles": 1,
"carbons": 3,
"hydrogens": 8
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/chem/oxygen-required-combustion", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"moles":1,"carbons":3,"hydrogens":8}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"moles":1,"carbons":3,"hydrogens":8}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/chem/oxygen-required-combustion", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"moles": 1,
"carbons": 3,
"hydrogens": 8
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "chem.oxygen_required_combustion",
"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
The engine applies the standard stoichiometric coefficient for O₂, which is x plus y over four, multiplies by the fuel moles, and reports oxygen_moles along with the per-mole O₂ coefficient and the ideal product moles of carbon dioxide and water.
What oxygen required for combustion means and what the response contains
This calculator returns the validated moles, carbons, and hydrogens, the derived o2_per_mole_fuel and oxygen_moles, the companion co2_moles and h2o_moles product amounts, a short formula_label such as C3H8, the precision used, a method tag oxygen_required_combustion, and a formula reminder. There is no mass-to-moles conversion for the fuel, no air-composition path that converts pure O₂ into dry-air volume, no heat-of-combustion path, and no general equation balancer for oxygenates or heteroatoms: the engine either applies the closed form for hydrocarbon CₓHᵧ inside the supported numeric range or rejects the input with invalid_input. Rejected cases include missing required fields, non-finite values, magnitudes above the documented ceiling, and any negative moles of fuel, because a negative fuel amount is not a physical combustion input.
How moles and atom counts are read and how results stay reproducible
Both atom counts must be finite and non-negative. 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 the amount of hydrocarbon is moles, but aliases n, n_fuel, moles_hydrocarbon, and amount are accepted so spreadsheets, query strings, and typed forms can reuse the same contract. The carbon atom count uses carbons with aliases C, carbon, carbon_atoms, and x; the hydrogen atom count uses hydrogens with aliases H, hydrogen, hydrogen_atoms, and y. Negative moles fails with invalid_input and a message that names the field so a bad cell does not become a silent negative oxygen demand. 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. Computation forms o2_per_mole_fuel equals carbons plus hydrogens divided by four, oxygen_moles equals moles times o2_per_mole_fuel, co2_moles equals moles times carbons, and h2o_moles equals moles times hydrogens divided by two. 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 x plus y over four coefficient yourself.
Where oxygen-for-combustion calculation fits in study, lab work, and software
Product and education tools use the endpoint when a learner types moles and a CₓHᵧ formula and the UI must show oxygen_moles with a clear intermediate o2_per_mole_fuel. 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 gas-volume or mass-to-mass stoichiometry helpers when you need related chemistry quantities, and with other science endpoints when you are building a small lab of free, deterministic combustion calculators.
Integration use cases
Deterministic test fixtures
Generate reproducible oxygen_moles and o2_per_mole_fuel for unit tests, chemistry tutors, and CI assertions on combustion stoichiometry.
Technical questions
How are moles of oxygen computed?
o2_per_mole_fuel = carbons + hydrogens/4, and oxygen_moles = moles × o2_per_mole_fuel, from CₓHᵧ + (x + y/4) O₂ → x CO₂ + (y/2) H₂O.