What is the percent yield formula?

Percent yield equals the actual yield divided by the theoretical yield, multiplied by 100. The actual yield is what you measured; the theoretical yield is the maximum predicted by the balanced equation.

Can percent yield exceed 100 percent?

In theory no, but a value above 100 percent usually signals an impure or wet product, or a weighing or measurement error.

How do I find the actual yield from percent yield?

Rearrange the formula: actual yield = (percent yield ÷ 100) × theoretical yield. Select "actual yield" in the tool and it does this for you.

How do I find the theoretical yield?

Theoretical yield = actual yield ÷ (percent yield ÷ 100), or actual ÷ percent × 100. It is the maximum mass of product the balanced equation allows from your limiting reactant.

What is the difference between actual and theoretical yield?

Theoretical yield is the amount of product predicted by stoichiometry assuming a perfect reaction. Actual yield is the amount you really recover, always equal to or less than theoretical because of side reactions, losses and incomplete reactions.

Do both yields need the same units?

Yes — use the same unit for both (usually grams or moles). Since percent yield is a ratio, the units cancel, so any consistent unit gives the same percentage.

What is the Percent Yield Calculator?

Free percent yield calculator using % yield = actual ÷ theoretical × 100. Solve for percent yield, actual yield, or theoretical yield. Runs entirely in your browser — nothing is uploaded. It runs free in your browser on Gera Tools, with nothing uploaded.

Percent Yield Calculator

Name: Percent Yield Calculator
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

Percent yield calculator

Percent yield measures how efficient a chemical reaction was by comparing the actual yield you recovered in the lab against the theoretical yield predicted by the balanced equation. It is a core quantity in stoichiometry, chemistry coursework and process work, where a low percent yield points to losses or side reactions.

How it works

The tool uses one relationship and rearranges it to solve for whichever value you leave blank:

percent yield     = actual ÷ theoretical × 100
actual yield      = (percent ÷ 100) × theoretical
theoretical yield = actual ÷ percent × 100

Choose the unknown from the dropdown, enter the two values you know, and the result appears instantly. Both yields must use the same unit; because it is a ratio, the units cancel.

Example

You expected 10 g (theoretical) and recovered 8.2 g (actual):

Percent yield: 8.2 ÷ 10 × 100 = 82%

Solving the other way — 82% yield with a 10 g theoretical gives 8.2 g actual; 8.2 g actual at 82% gives a 10 g theoretical.

Actual	Theoretical	Percent yield
8.2 g	10 g	82%
4.5 g	5 g	90%
9.9 g	10 g	99%

The calculation runs entirely in your browser and nothing is sent anywhere.

Why percent yield is rarely 100%

A perfect reaction — all limiting reagent consumed, all product collected — would give 100%. In practice several things reduce the recovery:

Side reactions. The limiting reagent reacts along a competing pathway, producing a different product that you discard.
Incomplete reaction. Equilibrium may prevent complete conversion, or the reaction may be stopped while some reagent remains.
Product lost during separation. Filtration, distillation, recrystallisation and extraction all leave some product behind in the apparatus, filtrate or wash.
Measurement errors. Imprecise weighing of the starting material inflates or deflates the theoretical yield calculation before you even start.

A percent yield above 100% is a diagnostic, not a result. It almost always means the product is wet (solvent trapped inside a crystalline product), an impurity is co-precipitating, or the theoretical yield calculation used the wrong molar mass.

Finding the theoretical yield first

Percent yield requires a theoretical yield, which you derive from stoichiometry before coming here. The steps are:

Write and balance the equation.
Convert the mass of the limiting reactant to moles using its molar mass.
Apply the mole ratio from the balanced equation to find moles of product.
Convert back to grams using the product’s molar mass.

For example: synthesising aspirin (acetylsalicylic acid, molar mass 180.16 g/mol) from 5.00 g of salicylic acid (molar mass 138.12 g/mol) in a 1:1 mole ratio gives a theoretical yield of 5.00 ÷ 138.12 × 180.16 = 6.52 g. If you recover 5.2 g, the percent yield is 5.2 ÷ 6.52 × 100 = 79.8%.

Using this tool to work backwards

The reverse calculation is equally useful in lab planning. If you need at least 2 g of product and your reaction typically runs at 75% yield, the required theoretical yield is 2 ÷ 0.75 = 2.67 g, which tells you how much limiting reagent to weigh out. Select “theoretical yield” in the dropdown, enter your target actual yield and the expected percent yield, and the tool solves for the theoretical yield you need to plan your synthesis around.