Stoichiometry Calculator — Moles, Mass, and Reaction Ratios

Stoichiometry is basically dimensional analysis applied to chemistry — once you understand mole ratios, everything else follows logically. The problem is that real problems have multiple steps and it's easy to drop a conversion factor halfway through. The CalcHub Stoichiometry Calculator walks through the chain of conversions and shows each step, which is genuinely useful when you're checking your work rather than just getting an answer.

What Stoichiometry Solves

Given a balanced chemical equation and the amount of one substance, stoichiometry lets you find:

• How many moles/grams of another substance are produced or consumed
• Which reagent runs out first (limiting reagent)
• Theoretical yield of a product
• Excess amount of the non-limiting reagent

The Mole Ratio is Everything

For the combustion of methane: CH₄ + 2O₂ → CO₂ + 2H₂O

The mole ratios directly from the coefficients:

Substance	Coefficient	Mole ratio relative to CH₄
CH₄	1	1 : 1
O₂	2	1 : 2
CO₂	1	1 : 1
H₂O	2	1 : 2

So burning 1 mol of methane produces exactly 2 mol of water.

How to Use the Calculator

1. Enter or paste the balanced equation into CalcHub.
2. Specify the known quantity — the substance you're starting with, and whether it's in grams or moles.
3. Select the target substance.
4. The tool calculates the conversion using: grams → moles (via molar mass) → mole ratio → moles of target → grams of target.

Worked Example

How many grams of CO₂ are produced by burning 32 g of methane (CH₄)?

Equation: CH₄ + 2O₂ → CO₂ + 2H₂O

Step 1: Grams of CH₄ to moles
32 g ÷ 16.04 g/mol = 1.995 mol CH₄

Step 2: Apply mole ratio (1:1 for CH₄ to CO₂)
1.995 mol CO₂

Step 3: Moles to grams of CO₂
1.995 × 44.01 = 87.8 g CO₂

Gram-to-Gram Conversion Shortcut

g of product = (g of reactant ÷ MM_reactant) × mole ratio × MM_product

It's one formula, but it hides three separate conceptual steps. The calculator shows them separately, which helps when you're learning.

Tips

• Always start with a balanced equation. Stoichiometry ratios come directly from coefficients. If your equation is unbalanced, your answers will be wrong even if the math is perfect.
• Units are your safety net. If you're doing this by hand, track units at every step. Wrong unit cancellation is the most common source of errors.
• Theoretical vs. actual yield. Stoichiometry gives theoretical yield (100% conversion). Real reactions rarely achieve this — that's where percent yield comes in.

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What if I don't know which reagent is limiting?

The calculator can find this for you — enter the amounts of all reactants and it identifies which one runs out first, then calculates yield based on that limiting amount.

Can I use this for reactions in solution (aqueous chemistry)?

Yes. For reactions in solution, convert concentration × volume to moles first (n = M × V), then apply the same mole ratio logic. The calculator accepts molarity and volume as input for this reason.

How is stoichiometry related to percent yield?

Stoichiometry gives you the theoretical maximum (assuming complete reaction). Percent yield = (actual yield / theoretical yield) × 100. If you produced 75 g but stoichiometry predicted 90 g, your percent yield is 83.3%.

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Related calculators: Limiting Reagent Calculator · Percent Yield Calculator · Molar Mass Calculator