To scale a recipe, divide the servings you want by the servings the recipe makes, then multiply every ingredient amount by that factor. Going from 4 to 6 servings gives a factor of 1.5, so 2 cups of flour becomes 3 cups and 1/2 tsp of salt becomes 3/4 tsp.
Home cooks feeding a bigger table, caterers stretching a tested formula and bakers halving a cake all face the same arithmetic: one factor applied to every line of the recipe. Paste the ingredient list, one item per line, set how many servings the recipe makes and how many you need, and the table shows each original amount beside its scaled amount. Mixed numbers, simple fractions, decimals and the ½ ¾ style characters are read, and results are rounded to the nearest common kitchen fraction so you can measure them with ordinary cups and spoons. Lines without a leading amount, such as a pinch of salt, are listed but left alone. The limit is chemistry, not arithmetic: leavening, salt, spices and cooking time do not always scale in a straight line, so very large or very small batches still need judgement.
Enter how many servings or portions the recipe states it makes.
Enter the target; quarter servings are allowed for fine adjustment.
Put one ingredient per line with the amount first, or open a plain text file with the list.
Each line shows the original amount and the scaled amount; unscaled lines are flagged in the warnings.
Result Scale factor: 2.5
Lines scaled: 2
Lines without an amount: 0
A factor of 2.5 turns 4 cups of stock into 10 cups and one onion into 2 1/2.
Result Scale factor: 1.5
Lines scaled: 3
Lines without an amount: 1
Every amount grows by half: 1/2 tsp salt becomes 3/4 tsp, and the pinch of pepper is left to taste.
Result Scale factor: 0.5
Lines scaled: 2
Lines without an amount: 0
A factor of 0.5 gives 1 1/2 eggs and 3/8 cup sugar; beat the eggs and measure half by weight.
factor = desired servings ÷ original servings; new amount = original amount × factor
factororiginal amountnew amountThis is the yield-conversion method taught in professional cooking courses. The factor is computed once, then every leading quantity is multiplied by it. Units are kept as written, so 3/4 cup stays in cups. Results within 0.02 of a familiar fraction (eighths, quarters, thirds, halves) are shown as that fraction; others are shown to two decimals, and amounts of 20 or more to one decimal.
It is the servings you want divided by the servings the recipe makes. Twelve servings from a recipe for eight gives 12 ÷ 8 = 1.5, and every amount is multiplied by 1.5.
Whole numbers (3), decimals (1.5 or 1,5), simple fractions (3/4), mixed numbers (1 1/2) and the single-character fractions ½, ⅓, ⅔, ¼, ¾ and the eighths. The amount has to be at the start of the line.
They appear in the table with no original amount and 'as needed' in the scaled column, and a warning counts them. Seasoning to taste is best adjusted at the end anyway.
If the scaled amount is not within 0.02 of an eighth, quarter, third or half, a fraction would misstate it, so the tool prints two decimals. For example 0.6 cups is shown as 0.6, which is closer to weighing than to a cup measure.
The ingredient ratios do, which is why bakers often work by weight. What changes is the pan: a doubled batter in the same pan is deeper and needs longer at a slightly lower temperature, or two pans instead of one.
Beat a whole egg and use half of it, about 25 g for a large egg of roughly 50 g without the shell. For 1 1/2 eggs, use one whole egg plus half of a beaten one.