The cup-size problem
Recipe writers don’t always specify which cup they mean. North American cookbooks default to the US cup (240 mL); Australian and New Zealand cookbooks use the metric cup (250 mL); old British cookbooks may still use the imperial cup (284 mL). The 4% difference between US and metric is small enough to ignore for most home cooking, but it matters for bread and pastry.
Why bakers weigh ingredients
A cup of flour can weigh anywhere from 100 g to 150 g depending on whether it was scooped, sifted, or spooned. That’s a 50% range. For brownies and casseroles it doesn’t matter; for sourdough and croissants it ruins the recipe. Professional bakers weigh dry goods in grams precisely because the cup-volume measurement is unreliable.
The tablespoon trap
Australia uses 20 mL tablespoons. Canada, the US, and the UK use 15 mL tablespoons. Most published recipes assume 15 mL unless they specify “Australian tablespoon” or “1 tbsp (20 mL)”. The difference is small for most ingredients but stacks up over a recipe with 5+ tablespoon measurements.