Stoichiometry Calculator

Stoichiometry ties together virtually every quantitative calculation in chemistry — from working out how much reactant you need to how many grams of product a synthesis will deliver. This calculator bundles six of the most common stoichiometric tools into a single client-side page so you can move through a problem from start to finish without switching tabs.

What the calculator covers

Molar mass and elemental composition. Enter any molecular formula — including compounds with nested brackets such as Fe2(SO4)3 or Ca(OH)2 — and the tool returns the molar mass in g/mol together with a breakdown of each element’s atomic mass contribution and mass-percentage share. Atomic masses come from the IUPAC 2021 standard atomic weights.

Moles, grams and particles. The mole bridge connects the macroscopic world (grams you can weigh) to the atomic world (individual molecules). The conversion relationships are:

• n (mol) = m (g) / M (g/mol) — grams to moles
• m (g) = n × M — moles to grams
• N = n × Nₐ — moles to particles (Nₐ = 6.022 × 10²³ mol⁻¹)

Limiting reagent and theoretical yield. For a two-reactant reaction the tool identifies which reagent runs out first (the limiting reagent), calculates the theoretical yield of the chosen product, and reports how much of the excess reagent is left unreacted. You supply the balanced-equation stoichiometric coefficients and the actual masses available.

Percent yield. Real reactions rarely achieve 100% yield. Enter the theoretical and actual yields in any consistent unit (g, mol, mL) and the tool computes % yield = (actual / theoretical) × 100.

Concentration (molarity). Four sub-modes cover the standard concentration manipulations: finding molarity from a dissolved mass and solution volume (c = n / V), finding moles from molarity and volume, finding the required volume for a target number of moles, and performing a dilution via the conservation law C₁V₁ = C₂V₂.

Ideal gas law (PV = nRT). Solve for any one of pressure P (kPa), volume V (L), moles n (mol), or temperature T (K) given the other three. R is fixed at 8.314 kPa·L/(mol·K), which is numerically identical to 8.314 J/(mol·K). If you supply a molecular formula the tool also reports the corresponding gas mass in grams.

How to work a stoichiometry problem step-by-step

A complete stoichiometry problem typically follows this path:

1. Balance the equation (this tool assumes you have done that; coefficients are inputs).
2. Convert given masses to moles using the molar mass mode or the moles/grams panel.
3. Identify the limiting reagent using the ratio of available moles to stoichiometric coefficients.
4. Calculate theoretical yield from the limiting reagent moles and the product’s stoichiometric coefficient.
5. Compare to actual yield to get the percent yield.

Worked example — Haber process

The Haber synthesis of ammonia: N₂ + 3 H₂ → 2 NH₃.

Suppose you have 28 g of N₂ and 6 g of H₂.

• Molar masses: N₂ = 28.014 g/mol; H₂ = 2.016 g/mol; NH₃ = 17.031 g/mol
• Moles available: N₂ = 28 / 28.014 = 1.0 mol; H₂ = 6 / 2.016 = 2.976 mol
• Product each could make (coefficients 1, 3, 2):
  • From N₂: (1.0 / 1) × 2 = 2.0 mol NH₃
  • From H₂: (2.976 / 3) × 2 = 1.984 mol NH₃
• Limiting reagent: H₂ (it can only make 1.984 mol NH₃)
• Theoretical yield: 1.984 × 17.031 g/mol = 33.8 g of NH₃
• If your actual yield is 29 g: % yield = (29 / 33.8) × 100 = 85.8 %

Enter these values in the calculator — it produces the same answer in milliseconds with full step-by-step working shown beneath the result.

Formula reference

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