The single strongest argument for weighing is flour, because a cup of it can vary by an amount large enough to change what comes out of the oven.
How Much It Varies
Flour is a powder that traps air, and how much air depends entirely on how it got into the cup.
Flour scooped directly from a bag compacts as the cup pushes through it. Flour spooned in lightly and levelled holds considerably more air. The difference between those two methods is routinely reported at twenty per cent or more.
Twenty per cent more flour in a cake batter is not a subtle change. It is the difference between tender and dry.
Making the Switch
The easiest transition is to weigh what you currently measure, once, and write it on the recipe.
Scoop your cup the way you always do, weigh it, and record that number. From then on your recipe is reproducible, whether or not the figure matches a conversion table.
A scale with a tare function makes this a single-bowl operation, and the flat platform models across the escali scale range are designed to sit under a mixing bowl for exactly this.
The Variables Nobody Controls
- Whether the flour was scooped, spooned or poured
- How firmly it was levelled
- Whether the bag was recently shaken or has been settling for weeks
- Ambient humidity, since flour absorbs moisture from the air
- Whether it was sifted before or after measuring
- The size of the cup itself, which differs between countries
None of those apply to a weight. Two hundred grams is two hundred grams in any kitchen, on any day, however the bag has been stored.
Why It Matters More in Some Recipes
Bread tolerates variation reasonably well, because dough is adjusted by feel and hydration can be corrected.
Cakes, pastry and biscuits do not. Those are chemistry rather than craft, and the ratio of flour to fat to sugar to liquid determines the structure. A twenty per cent error there produces a visibly different result.
Humidity Is Real
Flour is hygroscopic and gains and loses moisture with the air around it.
That changes both its weight for a given volume and how much liquid a dough needs. Bakers in humid climates use less water; the flour brought some with it.
Weighing removes the first problem and makes the second visible rather than mysterious.
The Reference Figures
Common conversions put a cup of plain flour somewhere around 120 to 130 grams, and bread flour a little higher.
Those are averages of a wide range rather than facts, which is the whole point.
Everything Else Follows
Once flour is weighed, weighing sugar, butter and liquid into the same bowl is faster than washing three cups.