Why scaling isn’t just multiplication
Most recipes scale cleanly between 0.5× and 2× of their original servings — a quarter recipe of brownies and a double batch of bolognese both behave predictably. Beyond that range, the chemistry starts to misbehave: yeasted breads need slightly less yeast at large scale, custards crack when oversized, and pan size has to grow non-linearly because surface area scales differently than volume.
Scale by ingredients vs scale by chemistry
This calculator does the easy half — scaling ingredient masses. The harder half is adjusting cooking time, oven temperature, and pan size. As a rule of thumb, double batches of cakes, breads, and pies typically benefit from a 25°F (≈15°C) lower oven and a longer bake time. Roasts and braises tolerate scaling much better.
Why we round to 1/8
Most kitchens don’t have measuring spoons finer than 1/8 teaspoon, and 1/16 differences in flour or sugar don’t change a recipe. Rounding to 1/8 keeps the output usable. For precision baking, weigh ingredients in grams instead — a digital scale eliminates the fractions problem entirely.