Cup measurements are imprecise and vary by ingredient — a cup of flour weighs less than half a cup of honey. Here's the conversion for 30+ common baking ingredients, and why weighing is always better.
American recipes use cups; the rest of the world uses grams. The problem is that cups measure volume, not weight — and the same cup holds very different weights of different ingredients. Here's the conversion table you need, and why a kitchen scale is the single best baking upgrade you can make.
The weight of a cup of flour varies enormously depending on how it's scooped. A "scooped" cup of plain flour might weigh 160g; a "spooned and levelled" cup might weigh 120g — a 33% difference that will noticeably affect your baked goods. Professional bakers everywhere use weight measurements for this reason.
A US cup = 240ml. A UK/metric cup = 250ml. The difference is only about 4%, which for most recipes is negligible. However, for large quantities, it adds up — if a recipe calls for 4 cups, that's a difference of 40ml (nearly 3 tablespoons), which can affect bread and pastry recipes.
A decent kitchen scale costs £8–15 and eliminates all conversion uncertainty. More importantly, it makes recipes repeatable — you'll achieve the same result every time because you're measuring actual mass, not volume affected by how tightly you pack the cup. Professional bakers consider this non-negotiable for good reason.