Reaction Yield & Limiting Reagent Calculator
Reaction yield calculator. Finds the limiting reagent, theoretical yield and percent yield from reactant moles, stoichiometry and the product. Educational.
Reaction Yield and Limiting Reagent Calculator
Enter the moles available and the balanced-equation coefficient for each reactant (leave a row's moles blank to skip it).
How to use the reaction yield calculator
Balance the equation first
You need the stoichiometric coefficients from the balanced chemical equation. Enter each reactant's coefficient alongside the moles you actually have.
Enter reactant moles
Type the moles available for each reactant (convert from grams using molar mass first if needed). Leave a row's moles blank to ignore it — two reactants is enough.
Enter the product details
Give the product's coefficient and molar mass, and optionally the actual yield you obtained, to get a percent yield.
Read limiting reagent and yields
The tool identifies the limiting reagent, computes the theoretical (maximum) yield, and, if you entered an actual yield, the percent yield. Verify with a worked calculation.
Limiting reagents and yield — how much can a reaction make?
The ingredient that runs out first
A chemical reaction consumes its reactants in fixed proportions set by the balanced equation, much like a recipe. If a recipe needs two eggs per cup of flour and you have ten eggs but only one cup of flour, the flour limits how many batches you can make — the extra eggs are left over. In chemistry, the reactant that runs out first is the limiting reagent, and it alone determines how much product can form; the others are in excess. Finding it is the key step in any yield calculation. The method is simple: for each reactant, divide the moles you have by its coefficient in the balanced equation, and the smallest of those ratios identifies the limiting reagent. That smallest ratio is the "extent of reaction" — the number of times the balanced equation can proceed with the amounts on hand. Multiplying it by the product's coefficient gives the moles of product, and multiplying by the product's molar mass converts that to a mass: the theoretical yield, the maximum the reaction could possibly produce if everything went perfectly.
Reality never quite reaches that maximum, which is where percent yield comes in. The percent yield is the actual amount of product you isolate divided by the theoretical yield, times one hundred. A reaction that theoretically makes 200 grams but from which you recover 150 grams has a 75% yield. Percent yield is the chemist's report card on a reaction: it captures losses to side reactions, incomplete conversion, material left behind during purification, and reactions that don't go fully to completion. Improving it — by optimising conditions, driving equilibria, or refining the workup — is much of the craft of practical synthesis.
"The limiting reagent is the ingredient that runs out first — and it alone sets the ceiling on how much product a reaction can make. Everything else is in excess, waiting on it."
Getting the calculation right
Two things make or break a yield calculation, and neither is the arithmetic. The first is the balanced equation: the coefficients are essential, because the limiting reagent is found from moles divided by coefficient, not from moles alone. A reactant present in larger moles can still be limiting if its coefficient is large. Forgetting to balance the equation, or balancing it wrongly, is the most common source of error. The second is unit conversion: you must work in moles, so masses have to be converted to moles using each substance's molar mass before comparing, and the final product moles converted back to a mass using the product's molar mass. This calculator works directly in moles for the reactants and converts the product to grams, so convert any masses to moles first. A few further cautions: theoretical yield assumes the reaction goes to completion by a single pathway, so it doesn't account for equilibria that stop short, competing side reactions, or impure reactants; and percent yields above 100% signal an error — usually impure or wet product, or a miscalculated theoretical yield — rather than magic. Use this tool to identify the limiting reagent and compute yields quickly while learning the stoichiometry, and check important calculations by hand or with validated software.
10 Facts About Reaction Yield
The limiting reagent runs out first and caps the product.
Find it from the smallest moles ÷ coefficient.
Other reactants are in excess.
Theoretical yield = the maximum possible product.
Theoretical = extent × product coeff × molar mass.
Percent yield = actual ÷ theoretical × 100.
You must balance the equation first.
Always work in moles, not grams.
Real yields fall short due to losses and side reactions.
A yield over 100% means an error (often impure product).
Frequently asked questions
The limiting reagent is the reactant that is completely consumed first, and it determines the maximum amount of product the reaction can make. The other reactants are left over in excess. You find it by dividing each reactant's moles by its coefficient in the balanced equation; the reactant giving the smallest result is the limiting reagent. Everything in the yield calculation flows from that smallest ratio.
Divide the moles you have of each reactant by its stoichiometric coefficient, and pick the smallest result. That reactant is limiting. It's important to divide by the coefficient, not just compare moles, because a reactant present in more moles can still be limiting if the equation needs it in a larger ratio. The calculator does this comparison for every reactant you enter and reports which one is limiting.
Theoretical yield is the maximum amount of product the reaction could make if it went perfectly to completion, calculated from the limiting reagent. Percent yield compares what you actually obtained to that maximum: actual yield divided by theoretical yield, times 100. Theoretical yield is a prediction; percent yield is the real-world performance, and it's always below 100% because of losses, side reactions, and incomplete conversion.
Because the coefficients from the balanced equation are exactly what you divide the moles by to find the limiting reagent, and what you multiply by to get product moles. Without correct coefficients the whole calculation is wrong. The coefficients encode the fixed mole ratios in which substances react. Balancing the equation is therefore the essential first step — the calculator assumes the coefficients you enter come from a correctly balanced equation.
Almost every real reaction yields less than the theoretical maximum. Reasons include side reactions that consume reactant into other products, reactions that reach equilibrium before completing, product lost during filtration, washing, or transfer, and impurities in the starting materials. Purification steps in particular sacrifice some product for purity. A high percent yield is a sign of an efficient, clean reaction and good technique; improving it is a central goal in practical synthesis.
Not in reality — it signals an error. A yield above 100% usually means the isolated product is impure or still contains solvent or water (so it weighs more than pure product would), or that the theoretical yield was miscalculated, often by getting the limiting reagent or coefficients wrong. If you see this, dry the product thoroughly, check its purity, and re-examine the stoichiometry. The calculator will report values over 100% so you can catch such mistakes.
Divide the mass in grams by the substance's molar mass in grams per mole. For instance, 10 g of a reactant with molar mass 40 g/mol is 0.25 mol. This calculator takes reactant amounts in moles, so convert any masses first (our molarity calculator can help). The product, by contrast, is entered with its molar mass so the tool can convert the calculated product moles back into a mass for the theoretical yield.
No. The theoretical yield assumes the reaction proceeds completely by a single pathway, consuming the limiting reagent entirely. Many real reactions reach an equilibrium and stop short, or split reactant between competing products. Those effects reduce the actual yield below the theoretical and are captured by the percent yield rather than the theoretical calculation. The tool gives the ideal maximum; the gap to reality is the percent yield's job to report.
Use it to check your reasoning and learn the method, but make sure your balanced equation and mole conversions are correct — those, not the arithmetic, are where errors hide. For graded coursework, show your full working, and for laboratory or process work, verify the stoichiometry carefully. This tool is educational and runs the standard limiting-reagent and yield calculation; confirming it by hand cements the understanding.
No. The values you enter are processed entirely in your browser. Nothing is sent to a server, stored, or shared, and no account is required. The calculation runs on your device only.
Related News
You may be interested in these recent stories from our newsroom.
No related news yet for this tool. Our editorial team publishes new pieces every week.
Browse all news →75 more free tools
Calculators, converters, security tools — no signup.