Mass-to-mass stoichiometry calculator
4 g of hydrogen give 36 g of water. Enter the reactant mass, both molar masses and the two coefficients from your balanced equation, and get the theoretical product mass with the moles in between. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Mass of the reactant
- 4
- Reactant molar mass
- 2
- Product molar mass
- 18
- Reactant coeff
- 2
- Product coeff
- 2
- Moles reactant
- 2
- Moles product
- 2
- Product mass
- 36
- Precision
- 10
This mass-to-mass stoichiometry calculator converts a known reactant mass into the theoretical product mass for a balanced chemical reaction. You supply the mass of reactant you have, the molar mass of that reactant, the molar mass of the product of interest, and the two stoichiometric coefficients that link those species in the balanced equation. The engine first forms moles of reactant as mass over molar mass, multiplies by the mole ratio of product coefficient over reactant coefficient, then multiplies by the product molar mass to obtain product mass. Classic classroom checks include four grams of hydrogen with molar mass two and coefficients two to two for water of molar mass eighteen yielding thirty-six grams of water, and one hundred grams of calcium carbonate of molar mass one hundred producing forty-four grams of carbon dioxide when coefficients are one to one. The engine uses only finite deterministic arithmetic with no network calls, no sampling, and no date-dependent shortcuts.
From grams of reactant to grams of product
Mass-to-mass stoichiometry is the everyday calculation that turns a weighed amount of one substance into the theoretical mass of another substance that a balanced chemical equation predicts. After the equation is balanced, the coefficients fix the mole ratio between species; molar masses convert between grams and moles on each side. In symbols, moles of reactant equal reactant mass divided by reactant molar mass, moles of product equal moles of reactant times the product coefficient over the reactant coefficient, and product mass equals moles of product times product molar mass.
Those three steps collapse to one closed form: product mass equals reactant mass times product molar mass over reactant molar mass times product coefficient over reactant coefficient. Zero reactant mass with positive molar masses and coefficients is valid and yields zero product mass.
Where mass-to-mass stoichiometry fits in study, lab work, and software
Students meet mass-to-mass problems when a textbook introduces mole ratios after balancing equations, when a homework set gives grams of reactant and asks for grams of product, or when a contest problem expects a theoretical yield without a multi-step calculator that silently drops a coefficient. Teachers can pre-generate answer keys for modest molar masses and integer coefficients without trusting opaque apps that mix percent yield with theoretical mass or assume wrong units.
Lab technicians and preparers use the same map when a protocol requires a stated product mass from a weighed starting material and only a balance and a balanced equation are available: convert mass to moles, apply the coefficient ratio, convert back to mass, and confirm the planned yield. Developers call the same contract from scripts to seed deterministic test vectors for chemistry tutors, to normalize user-entered reaction parameters before a lab notebook export, or to satisfy programming-challenge statements that demand product grams rather than a hand-waved sketch.
What you can do with it
Homework and theoretical yield checks
Convert textbook reactant masses into theoretical product mass using molar masses and balanced coefficients before grading or graphing.
Lab prep and education software
Plan product masses from weighed reactants and balanced equations in lab notebooks, tutoring UIs, and automated worksheet generators.
FAQ
What does the mass-to-mass stoichiometry calculator cost?
It is free in your browser on this page.
How is product mass calculated?
Equivalently: moles of reactant from mass over molar mass, scale by the mole ratio, then multiply by product molar mass.
What happens if a molar mass is zero?
Zero or negative molar mass cannot convert between mass and moles for the reactant or product.
Does this tool find the limiting reactant?
No. It maps one reactant mass to one product mass using the coefficients you supply. Limiting-reactant search across several reagents is a different calculation.
Why are results rounded to a precision?
Default precision is 10 decimal places; you can set precision from 0 to 15.
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/mass-to-mass-stoich \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"reactant_mass":4,"reactant_molar_mass":2,"product_molar_mass":18,"reactant_coeff":2,"product_coeff":2}'const res = await fetch("https://api.kit.forhosting.com/chem/mass-to-mass-stoich", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"reactant_mass": 4,
"reactant_molar_mass": 2,
"product_molar_mass": 18,
"reactant_coeff": 2,
"product_coeff": 2
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/chem/mass-to-mass-stoich",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"reactant_mass": 4,
"reactant_molar_mass": 2,
"product_molar_mass": 18,
"reactant_coeff": 2,
"product_coeff": 2
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/chem/mass-to-mass-stoich", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"reactant_mass":4,"reactant_molar_mass":2,"product_molar_mass":18,"reactant_coeff":2,"product_coeff":2}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"reactant_mass":4,"reactant_molar_mass":2,"product_molar_mass":18,"reactant_coeff":2,"product_coeff":2}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/chem/mass-to-mass-stoich", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"reactant_mass": 4,
"reactant_molar_mass": 2,
"product_molar_mass": 18,
"reactant_coeff": 2,
"product_coeff": 2
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "chem.mass_to_mass_stoich",
"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 mass-to-mass stoichiometry means and what the response contains
This calculator returns the validated reactant mass, both molar masses, both coefficients, the intermediate mole amounts of reactant and product, the computed product mass, the precision used, a method tag mass_to_mass_stoich, a short formula reminder, and a unit hint that product mass shares the same mass unit as the input reactant mass. There is no multi-reactant limiting-reagent search, no percent-yield path, and no equation balancer: the engine either evaluates the mass-to-mass map 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, negative reactant mass, and any molar mass or stoichiometric coefficient that is zero or negative, because zero molar mass cannot convert mass to moles and a non-positive coefficient makes the mole ratio undefined or non-physical.
How mass, molar masses, and coefficients are read and stay reproducible
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 known mass is reactant_mass, but aliases mass, m_reactant, reactantMass, and mass_reactant are accepted so spreadsheets, query strings, and typed forms can reuse the same contract. Reactant molar mass is reactant_molar_mass with aliases mm_reactant, reactant_mm, M_reactant, and reactantMolarMass; product molar mass is product_molar_mass with aliases mm_product, product_mm, M_product, and productMolarMass. Both molar masses must be strictly positive finite numbers in grams per mole or any mass-per-mole unit consistent with the mass unit you chose for reactant_mass. Stoichiometric coefficients use reactant_coeff and product_coeff, with aliases such as coeff_reactant, n_reactant, reactantCoeff, and a for the reactant side, and coeff_product, n_product, productCoeff, and b for the product side. Coefficients must be positive; zero fails with invalid_input and a message that names the field so a bad cell does not become a silent division by zero. 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 mass-to-mass formula yourself.
Where mass-to-mass stoichiometry fits in study, lab work, and software
Product and education tools use the endpoint when a learner types reactant mass, molar masses, and coefficients and the UI must show product mass 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 molar concentration or gas volume helpers when you need related chemistry quantities, and with other science endpoints when you are building a small lab of free, deterministic stoichiometry calculators.
Integration use cases
Deterministic test fixtures
Generate reproducible product_mass and mole intermediates for unit tests, chemistry tutors, and CI assertions on mass-to-mass stoichiometry.