All calculatorsMolar Ratio Calculator
Compute stoichiometric molar ratios from a balanced reaction and convert a known amount of one species to another. Enter coefficients and (optionally) amounts in mol or g (with molar mass). See steps and a mini ratio chart.
Background
For a balanced reaction like aA + bB → cC + dD, the molar ratio between any two species is given by the ratio of their stoichiometric coefficients (e.g., C:A = c:a). To convert amounts, first express the known amount in moles, then scale by the coefficient ratio.
How this calculator works
- Enter species with role (reactant/product) and coefficient from the balanced reaction. Optionally include an amount for any species (in mol or g with molar mass).
- Choose a From species (with a known amount) and a To species.
- The conversion uses nto = nfrom × (coeffto/coefffrom). If Report to mass is checked and M is known for the To species, we also show grams.
Formula & Equation Used
Molar ratio: for species X and Y, ratio = coeffX : coeffY.
Conversion: nto = nfrom × (coeffto / coefffrom).
Mass <→ moles: n = m / M, m = n × M.
Example Problems & Step-by-Step Solutions
Example 1 — N₂ + 3H₂ → 2NH₃
Given 0.60 mol H₂. Ratio NH₃:H₂ = 2:3.
n(NH₃) = 0.60 × (2/3) = 0.40 mol.
Example 2 — C₃H₈ + 5O₂ → 3CO₂ + 4H₂O
Given m(CO₂) = 44.0 g; M(CO₂) ≈ 44.01 g·mol⁻¹ → n(CO₂) ≈ 1.000 mol.
Ratio O₂:CO₂ = 5:3 → n(O₂) = 1.000 × (5/3) = 1.667 mol.
Example 3 — A + 2B → 3C
Given 0.25 mol A; ratio C:A = 3:1 → n(C) = 0.25 × 3 = 0.75 mol.
Frequently Asked Questions
Q: Do I have to enter grams or moles?
Either is fine. If you enter grams, also provide the molar mass so we can convert to moles.
Q: What if my equation isn’t balanced?
Balance it first. Molar ratios depend on the stoichiometric coefficients from a balanced equation.
Q: Can I get the answer in grams?
Yes—check “Report to mass (g)” and provide the molar mass for the target species.
