Theoretical Yield Calculator

Convert the limiting reagent to moles, multiply by the mole ratio of product to reagent from the balanced equation, then multiply by the product's molar mass. Only the limiting reagent matters; the excess reagent has no say in the answer.

The product is not dry, or it contains unreacted starting material or solvent. Yields above 100% are not chemically possible, so treat one as a signal to dry the sample to constant weight and reweigh it.

It depends on the reaction. Above 90% is excellent for a simple single-step reaction; a multi-step synthesis where each step runs at 80% ends at 51% after three steps, and that is normal.

Reactions rarely go to completion, side reactions consume starting material, and product is lost in every transfer, filtration and recrystallisation. The theoretical figure assumes none of that happens.

The limiting reagent, always. It runs out first and stops the reaction, so it caps the product no matter how much of the other reagent is present.

The coefficients from the balanced equation. Subscripts describe what is inside one molecule; coefficients describe how many molecules react, and the ratio between coefficients is what scales the moles.

Divide each reactant's moles by its coefficient in the balanced equation and take the smallest result. Comparing masses does not work, and comparing moles without dividing by the coefficients does not work either.

Percent yield measures how much of the theoretical product you actually recovered. Atom economy measures how much of the reactant mass ends up in the desired product rather than in by-products, and it is fixed by the equation before any experiment happens.

Losses that are fixed rather than proportional — film left on glassware, product held in a filter cake, material lost to a transfer — take a much larger share of a 100 mg reaction than of a 100 g one. Milligram-scale chemistry routinely reports lower yields for this reason alone.

Yes, if you convert with the density first. Volume times density gives mass, then mass over molar mass gives moles. Densities are temperature-dependent, so a value measured at 20 °C is slightly off in a warm laboratory.

Not the theoretical yield, which depends only on the limiting reagent. It can affect the actual yield by driving an equilibrium reaction further towards products, which is exactly why the cheap reagent is usually the one in excess.

On purified product, and the purification method should be stated with it. A crude yield includes solvent and impurities and is not comparable to anything, which is why it is rarely worth quoting on its own.