• Eggs round to whole numbers — half an egg is awkward. If scaling gives you 1.5 eggs, lightly beat 2 eggs and use 75% by weight, or just round up and add 1 tbsp extra flour.
• Leavening agents (baking powder / bicarb) don't scale perfectly linear at large multipliers. For 3× or more, reduce raising agent by about 10–15% to avoid a metallic taste.
• Bake time stays roughly the same. A bigger batch means more trays, not longer baking. Rotate trays halfway if your oven has hot spots.
• Tin size matters. Scaling a 12-cake recipe to make a single sponge? Bake time will increase significantly — use a skewer test.
• Salt & vanilla can stay slightly under the scaled amount. They intensify in larger batches.