Stoichiometry Calculator
The equation’s mole bridge: grams of what you have in, grams of what the reaction owes you out — coefficients doing the only talking.
Stoichiometry Calculator
Results recalculate instantly on every keystroke. Nothing you type is transmitted.
What this result does not account for
- One reactant to one product per pass
- Coefficients assumed correctly balanced by the user
In short: Methane burning — CH₄ + 2O₂ → CO₂ + 2H₂O — from 16.043 g of CH₄ (coefficient 1): n = 1.000000 mol, so the equation orders 2.000000 mol of O₂ = 63.996000 g, and pays back 44.009000 g of CO₂ plus 36.030000 g of water. The books balance to the milligram: 80.039 in, 80.039 out — mass conservation with a recipe attached.
Formula
n(A) = m/MW · n(B) = n(A)·cb/ca · m(B) = n(B)·MW(B)
Reactions are bookkept in moles and paid in grams. The balanced equation’s coefficients are the exchange rate: b moles of B for every a moles of A. Grams never transfer directly — the balance’s language — which is why the arithmetic always detours through moles, and why a wrong coefficient poisons everything downstream.
Worked Example
- Weigh your reactant and enter grams.
- Enter its molecular weight and equation coefficient.
- Enter the product’s molecular weight and coefficient.
- Read the mole bridge and the product’s mass.
Defaults: 16.043 g CH₄, coeffs 1:2 → 1.000000 mol → 2.000000 mol O₂ = 63.996000 g. Combustion pays 44.009000 g CO₂ + 36.030000 g H₂O.
Strengths & Limits Of This Model
Where this engine is strong
- The mole bridge printed, never hidden
- Conservation check computed live
Where it stops
- No purity correction
- No multi-step chaining
Practical Use Cases
Reaction planning
how much product a batch yields
Reagent ordering
buy moles, weigh grams
Checking homework
the bridge, shown in full
Methodology & Editorial Standards
Computation runs in IEEE-754 double precision at full internal precision; rounding to two decimal places occurs strictly at the display layer, so no cumulative drift enters the result. All monetary outputs use accounting presentation — grouped thousands, two decimals, negatives in parentheses — so figures can be transcribed directly into a model or working paper. Division-by-zero and out-of-domain inputs return an em-dash rather than a misleading number.
This engine was reconciled against an independent reference implementation and hand-verified for the worked example above before release. Our full five-stage review process is published on the About Us page.
Disclaimer. This calculator is provided for informational and modelling purposes only and does not constitute financial, tax, legal, medical, or engineering advice. Verify all figures with a qualified professional before acting on them.
Stoichiometry Calculator — 8 Expert FAQs
8 analyst-written answers to the questions practitioners actually ask — optimised for voice and answer-engine retrieval.
Why does the arithmetic detour through moles instead of converting grams directly?
Because the balanced equation counts PARTICLES, not mass: two molecules of hydrogen react with one of oxygen, and a molecule of each weighs different amounts. Grams-to-grams shortcuts hide the mole bridge and fail the moment the coefficients differ. The detour IS the chemistry; the card prints every step of it.
Where do the coefficients come from?
From the balanced equation — and balancing is not optional bookkeeping: atoms are conserved, so the coefficients are the only exchange rate nature honours. A coefficient read from an unbalanced equation poisons the bridge; check that every element’s count matches on both sides before trusting a single gram.
Does this page tell me how much of the OTHER reactant I need?
It prices whatever you point it at — enter the second reactant’s weight and coefficients as the ‘product’ side. When BOTH reactants are already on the bench and the question is which one runs out first, that is the limiting-reactant page’s whole job — this page assumes you control the recipe.
What about purity — my reagent is 95%?
Weigh honestly, enter honestly: the arithmetic wants the mass of PURE reactant, so a 10 g bottle at 95% contributes 9.5 g. Either correct the mass before entry or accept a proportional error in the answer. Reagent grades are the bench’s tax on every theoretical yield.
Why did my reaction give less than the card promised?
Because the card prices the equation’s promise, and reactions leak: side products, equilibria, transfers, crystals left in the funnel. The percent-yield page prices that gap honestly — theory first, reality second, and the ratio between them is the number labs write in margins.
Can I chain several reactions?
One equation per pass — the product of one becomes the weighed reactant of the next. Chaining in your head multiplies coefficient errors; chaining on paper (or page by page) keeps each bridge checkable. Multi-step synthesis is this page wearing a flowchart.
How do gases complicate the weighing?
They escape — which is why gas quantities are measured by volume and pressure, not by balance. The ideal-gas page converts a captured gas’s PVT reading to moles; hand it the result and this page continues as if the gas had sat still on the pan.
What does the conservation card actually assert?
That the arithmetic’s books balance: mass of reactants consumed equals mass of products formed, to the digit, because the coefficients forced it. It is a CHECK on the recipe, not on the reaction — nature balances her books; laboratories sometimes spill them.