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Stoichiometry Calculator

The Stoichiometry Calculator uses mole ratios from balanced chemical equations to determine the amounts of reactants and products. Calculate theoretical yield, identify limiting reagents, and convert between moles, grams, and liters for any reaction.

Stoichiometry Calculator — Live Preview
Moles Product
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Proportion Solver
A : B = C : D — Enter any 3 values
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Visual ratio breakdown
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    Ratio Simplifier
    Reduce any ratio to its simplest form
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    Simplified Result
    Reduced to lowest terms
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      Ratio Scaler
      Multiply a ratio by a scale factor
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      Scaled Result
      Ratio after scaling
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        What is Stoichiometry?

        Stoichiometry is the calculation of quantities in chemical reactions based on balanced equations. The coefficients in a balanced equation give the mole ratio — for 2H₂ + O₂ → 2H₂O, the ratio is 2:1:2, meaning 2 moles of hydrogen react with 1 mole of oxygen to produce 2 moles of water.

        Stoichiometric calculations are essential in chemistry for determining how much reagent is needed, predicting product yields, identifying limiting reagents, and calculating percent yield. The mole ratio is the bridge between reactants and products.

        Formulas & Equations Used

        This Stoichiometry Calculator uses the following core equations:

        1 Mole Ratio Conversion ▼
        Moles Product = Moles Reactant × (Coefficient Product / Coefficient Reactant)

        For 2H₂ + O₂ → 2H₂O: 3 moles H₂ produces 3 × (2/2) = 3 moles H₂O.

        2 Moles from Grams ▼
        Moles = Mass (g) / Molar Mass (g/mol)

        36 grams of water (H₂O, MW=18): Moles = 36 / 18 = 2 moles.

        3 Theoretical Yield ▼
        Theoretical Yield = Moles Limiting Reagent × Mole Ratio × Molar Mass Product

        Determines the maximum possible product from the limiting reagent.

        How to Use This Stoichiometry Calculator

        Follow these 3 simple steps:

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        Enter Your Values

        Type the known values into the input fields above. The Stoichiometry Calculator accepts any positive numbers.

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        Choose Calculation Mode

        Select Solve, Simplify, or Scale mode in the calculator. Each applies different equations to your inputs.

        3

        View Results

        Click Calculate to see your answer with a visual ratio bar, pie chart, and step-by-step solution breakdown.

        Example Problems & Step-by-Step Solutions

        Here are 3 worked examples using this Stoichiometry Calculator:

        Example 1 How much O₂ needed to react with 4 moles H₂?
        1 Equation: 2H₂ + O₂ → 2H₂O
        2 Mole ratio H₂:O₂ = 2:1
        3 O₂ needed = 4 × (1/2) = 2 moles
        4 Mass: 2 × 32 g/mol = 64 grams O₂
        ✓ 2 moles (64 grams) of O₂ needed
        Example 2 Theoretical yield from 10g CH₄ burning in excess O₂
        1 CH₄ + 2O₂ → CO₂ + 2H₂O
        2 Moles CH₄ = 10g / 16 g/mol = 0.625 mol
        3 Moles CO₂ = 0.625 × (1/1) = 0.625 mol
        4 Mass CO₂ = 0.625 × 44 = 27.5 g
        ✓ Theoretical yield: 27.5 g CO₂
        Example 3 Find limiting reagent: 5 mol H₂ and 4 mol O₂
        1 2H₂ + O₂ → 2H₂O
        2 H₂ needs: 5/2 = 2.5 mol O₂ (have 4, sufficient)
        3 O₂ needs: 4×2 = 8 mol H₂ (have 5, insufficient)
        4 H₂ is the limiting reagent
        ✓ H₂ is the limiting reagent; 1.5 mol O₂ excess

        Frequently Asked Questions

        What is a mole ratio? ▼

        A mole ratio is the ratio of coefficients in a balanced equation. For N₂ + 3H₂ → 2NH₃, the mole ratios are N₂:H₂ = 1:3, H₂:NH₃ = 3:2, and N₂:NH₃ = 1:2.

        What is a limiting reagent? ▼

        The limiting reagent is the reactant that runs out first, determining the maximum product yield. The other reactant is 'in excess.' Identify it by dividing each reactant's moles by its coefficient — the smallest quotient is the limiting reagent.

        How do you calculate percent yield? ▼

        Percent Yield = (Actual Yield / Theoretical Yield) × 100. If you expected 50g of product but obtained 42g: Percent Yield = (42/50) × 100 = 84%.

        Why must chemical equations be balanced for stoichiometry? ▼

        Balanced equations obey the law of conservation of mass — atoms are neither created nor destroyed. Unbalanced equations give incorrect mole ratios and wrong calculations.

        How do you convert between moles and grams? ▼

        Multiply moles by molar mass to get grams. Divide grams by molar mass to get moles. Example: 3 moles of NaCl (MW=58.44) = 3 × 58.44 = 175.3 grams.

        Learn About Ratios

        What is a ratio?

        A ratio is a comparison between two or more quantities showing the relative size of one to another. Written as A : B, it means 'for every A units of the first quantity, there are B units of the second.' For example, a ratio of 3 : 4 means for every 3 parts of A, there are 4 parts of B. Ratios are used in cooking, construction, finance, science, and everyday life.

        How do I solve a proportion?

        A proportion is an equation that says two ratios are equal: A : B = C : D. To solve for a missing value, use cross-multiplication. If D is unknown: D = (B × C) / A. This works because in equal ratios, the cross products are always equal: A × D = B × C. Our Proportion Solver does this automatically — just enter any 3 values and it finds the 4th.

        How do I simplify a ratio?

        To simplify a ratio, find the Greatest Common Divisor (GCD) of both numbers and divide each by it. For example, 24 : 36 — the GCD of 24 and 36 is 12. So 24 ÷ 12 = 2 and 36 ÷ 12 = 3, giving the simplified ratio 2 : 3. Our Simplifier automatically finds the GCD and reduces your ratio to its lowest terms.

        What is ratio scaling and when is it useful?

        Scaling a ratio means multiplying both parts by the same factor to create an equivalent, larger (or smaller) ratio. For instance, scaling 2 : 5 by a factor of 3 gives 6 : 15. This is extremely useful for recipes (tripling a recipe), construction (scaling blueprints), mixing solutions, or any scenario where you need to maintain the same proportion at a different magnitude.

        What's the difference between a ratio and a fraction?

        A ratio A : B compares two quantities to each other (part-to-part), while a fraction A/B typically represents a part-to-whole relationship. However, any ratio can be expressed as a fraction: 3 : 4 is equivalent to 3/4 = 0.75. The key difference is context — ratios compare quantities side-by-side, while fractions represent a portion of a total.