How this instrument works
In stoichiometry, theoretical yield is the maximum mass of product a reaction could produce if every bit of the limiting reagent converted perfectly, with no losses. Actual yield is what a chemist really weighs out on the balance after running the reaction and purifying the product. Percent yield is the ratio between the two, expressed as a percentage, and it is the standard way chemists report how well a reaction — or a particular attempt at it — performed. This instrument runs that relationship in reverse: given a percentage and a theoretical maximum, it returns that resulting mass in grams.
Real reactions almost never hit 100% efficiency. Side reactions consume some of the limiting reagent on unwanted pathways, equilibrium reactions stop short of complete conversion, and purification steps — recrystallization, filtration, extraction, distillation — lose product at every transfer. A percent yield in the 70-90% range is common and often considered good for a multi-step synthesis; percent yields above 95% are notable, and a reported figure above 100% signals a measurement or purity problem (often residual solvent or an impure product), not a reaction that beat its own stoichiometric ceiling.
This calculator is most useful for planning: if a literature procedure reports an 85% yield for a reaction whose theoretical maximum you have already calculated from your own reagent quantities, multiplying the two tells you how much product to expect to isolate before you even start the synthesis — useful for deciding whether a reaction is worth running on the scale you have reagents for.
- Enter Percent yield (%) — a literature-reported figure, a target you're aiming for, or a yield measured in a previous run.
- Enter Theoretical yield (g) — the maximum mass calculated from the balanced equation and the limiting reagent's moles.
- Read Actual yield (g) directly — it updates the instant either field changes.
- To go the other direction and find percent yield from a measured actual yield, divide your measured mass by the theoretical yield and multiply by 100 by hand; this instrument solves specifically for actual yield.
- Both inputs must be zero or greater — a negative yield or negative mass has no chemical meaning, so the instrument will not compute one.
Worked example — an 85% yield of an 88.02 g maximum
A synthesis has a calculated theoretical yield of 88.02 g, and the procedure being followed reports an 85% yield for this step. Enter 85 into Percent yield (%) and 88.02 into Theoretical yield (g); Actual yield (g) reads 74.817 — found by taking 85/100 = 0.85 and multiplying it by 88.02 g.
That 74.817 g is the mass a chemist following this procedure should reasonably expect to isolate after the reaction and purification are complete — useful for judging beforehand whether the batch will provide enough product for the next step, without having to run the reaction first.
Questions
What's the difference between theoretical yield and actual yield?
Theoretical yield is the maximum mass of product possible from the limiting reagent, calculated purely from stoichiometry with no losses. Actual yield is the mass a chemist actually isolates after running and purifying the reaction. Actual yield is virtually always lower than theoretical yield, because real reactions have side reactions, incomplete conversion, and purification losses that a stoichiometric calculation can't predict — percent yield is simply the ratio of the two, expressed as a percentage.
Can percent yield ever be over 100%?
Not honestly, no — 100% represents perfect conversion of the limiting reagent with zero loss, so a genuine result can't exceed it. A calculated percent yield above 100% almost always means the isolated product wasn't pure: leftover solvent, unreacted starting material, or an inorganic salt weighed along with the product will inflate the measured mass beyond what the pure compound alone would weigh.
Why is actual yield usually lower than theoretical yield?
Because real reactions lose material at several points that a stoichiometric calculation ignores: side reactions divert some of the limiting reagent to other products, many reactions don't run to full completion, and every purification step — filtration, recrystallization, extraction, distillation — leaves some product behind on glassware, in a mother liquor, or in a discarded fraction. Each of those losses lowers actual yield without lowering theoretical yield, which is calculated purely from the balanced equation.
How do I calculate the theoretical yield this instrument needs as an input?
Convert the limiting reagent's mass to moles, use the balanced equation's mole ratio to find moles of product, then convert that back to grams using the product's molar mass. This instrument starts from that already-calculated theoretical yield figure rather than recomputing it, since it needs the full balanced equation and every reagent quantity, which vary reaction to reaction.
What percent yield counts as 'good' for a synthesis?
It depends heavily on the reaction, but as a rough guide, 70-90% is common and often considered solid for a straightforward single-step reaction, while multi-step syntheses compound losses at every step and can have an overall efficiency well below any single step's figure. A simple acid-base or precipitation reaction might reasonably reach 95%+, while a reaction prone to side products or a difficult purification might be considered successful in the 50-70% range.
Does this instrument work for any units of mass, not just grams?
The formula itself is unit-agnostic — actual yield comes out in whatever mass unit you entered for theoretical yield, since percent yield is a dimensionless ratio. This instrument's field is labeled in grams because that's the most common lab-scale unit, but you can enter a theoretical yield in milligrams or kilograms and read the actual yield back in that same unit.