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2.5 cups of flour at 1.5× becomes 3¾ cups — every line scaled, snapped to the fractions measuring cups actually have.
Scaling a recipe means multiplying a dozen lines without a single arithmetic slip — and rounding to fractions that exist on a measuring cup. Paste the ingredient list, set the scale (0.5 halves, 2 doubles, 1.5 feeds six instead of four), and every quantity is scaled and snapped to kitchen fractions automatically.
Cooks use it when the guest list doubles: paste the ingredient lines, set 1.5×, and 2.5 cups of flour becomes 3¾ — snapped to real kitchen fractions.
No — and the exceptions are where doubled recipes fail. Scale fully: flour, sugar, liquids, butter. Scale cautiously: salt (scale to 1.5× on a double, taste up), spices and chili (heat compounds — 1.5× on a double), leavening (baking powder/soda at 1.75× for a double — over-leavened batter collapses), and yeast (1.5× is usually plenty). Don't scale at all: cooking time — a doubled casserole is deeper, not twice as hot, so it needs ~50% more time at the same temperature, and doubled cookies bake in the same minutes on two sheets. Eggs are the awkward unit: 1.5× on a 2-egg recipe means 3 eggs, but 0.75× on 2 eggs means beating one and weighing out half (~25 g).
Pan area scales with the square of diameter — the most-missed math in baking. An 8-inch round pan holds 50 sq in of batter; a 9-inch holds 64 (28% more); a 9×13 pan holds 117 sq in. So 1.5× an 8-inch recipe fits a 9-inch perfectly, and doubling an 8-inch round recipe fits a 9×13 rectangle. Depth matters as much as area: batter deeper than the original bakes slower in the center — drop the oven 25°F and extend time rather than cranking heat. The batter-depth rule: keep the scaled batter the same depth as the original and baking time stays nearly identical. Springform and bundt pans are volume-first: a 10-inch bundt holds about 12 cups of batter; never fill any pan past two-thirds.
Because a "cup of flour" varies by 30% depending on how it is scooped — dipping the cup packs flour to 140–160 g, spooning and leveling gives the standard 120 g. That variance is bigger than recipe scaling errors, which is why professional baking runs entirely in grams: 500 g of flour is 500 g every time, in any kitchen, with any scoop. Volume is fine for liquids (water and milk are consistent) and tolerant ingredients, but flour, cocoa, and powdered sugar compress. The conversion discipline: use the cups-to-grams converter with spooned-and-leveled values, weigh once, write the grams on the recipe card — and every future batch is identical. A $15 scale eliminates the single largest source of baking inconsistency.