Find the batch factor
Decide what the recipe’s yield means before changing it. Twelve cookies and eighteen cookies can be compared if you intend to keep each cookie the same size. Twelve small portions and eighteen large portions are not the same scaling problem.
For a recipe that makes 12 equal portions, a target of 18 gives 18 ÷ 12 = 1.5. Multiply each ingredient mass by 1.5. To reduce a four-portion recipe to one portion, the factor is 1 ÷ 4 = 0.25. A factor below one reduces the batch; a factor above one increases it.
Work through the ingredient list
Consider an arithmetic example with 250 g flour, 150 g sugar and 100 g egg mass. At a factor of 1.5, those values become 375 g, 225 g and 150 g. The original total is 500 g and the new total is 750 g.
The ratio of sugar to flour remains 150 ÷ 250 = 0.6 in the original and 225 ÷ 375 = 0.6 in the larger batch. That is a useful way to check that one line has not been left unscaled. Our tool preserves the unrounded values for its total and rounds only what you see in the table.
These ingredient numbers demonstrate the calculation. They do not describe a tested bake or promise a particular texture or baking result.
Use one mass unit for the whole list
The calculator accepts grams or weight ounces. Switching units converts the existing physical mass; it does not interpret an ounce as a fluid ounce. A gram amount and a cup amount cannot be added into one meaningful mass total without ingredient-specific information.
King Arthur’s ingredient chart lists separate volume and weight equivalents for different ingredients. That distinction matters: there is no universal “grams in a cup” value for everything in a recipe. If the original recipe provides weights, use them. If it only provides volume, establish an appropriate ingredient-specific conversion before entering the list.
Round once, at the weighing step
A calculation might produce 3.75 g for a small ingredient. The tool can display that number; it cannot decide whether your scale can measure it reliably. Keep the calculated target in your notes and make any practical rounding decision deliberately. Avoid rounding the factor before multiplying each row.
Scaling quantities does not scale every part of a method. Mixer capacity, tray count, pan dimensions and timing may need separate decisions. The tool does not predict baking time, temperature, food safety or whether a very large or very small version behaves like the original recipe.
References & further reading
These references support the ingredient and pan context. The worked numbers and diagrams above are our own explanatory examples.