There is no single grams-to-cups answer
A cup is a measure of volume, a gram is a measure of weight, and the bridge between them is density — which is a property of the ingredient, not of the cup. This is why “how many grams in a cup” has no universal answer, and why any converter that gives you one is wrong for most ingredients.
The spread is wide. One US cup holds about 85 g of cocoa powder, 125 g of all-purpose flour, 200 g of granulated sugar, 227 g of butter and 340 g of honey. Using a flour figure for honey would put you out by a factor of nearly three.
Why flour is the worst offender
Flour compresses. Scooping the cup straight into the bag packs it down and can pick up 150 g or more where a spooned-and-levelled cup gives 125 g — a 20% error, which in a cake is the difference between tender and dry. The figures here assume the spoon-and-level method, which is what recipe developers generally test with.
This is also the argument for buying a kitchen scale. Weight is unambiguous: 125 g of flour is 125 g however it is packed, whereas a cup of it is a range. Professional and European recipes are written by weight for exactly this reason.
Reading the fractions
Results are given as measuring-cup fractions where one fits closely — halves, thirds, quarters and eighths, because that is what a real measuring set contains. Where nothing sensible fits, the decimal is shown instead and the tablespoon row is usually the more practical answer: 1 tablespoon is a sixteenth of a cup.