Volume and weight aren't the same thing, and the ratio between them is different for every ingredient - so a generic converter genuinely can't help here. Pick the actual ingredient and get the real weight, not an approximation.
A cup measures volume - how much space something takes up. Grams measure weight. The only way to convert between them is to know the ingredient's density, and that's wildly different from one ingredient to the next: a cup of honey (about 340g) weighs nearly four times what a cup of cocoa powder (about 85g) does, in the exact same cup. Water happens to weigh close to what people assume "a cup" should weigh (about 237g) - which is probably where the myth that "a cup is always about 240g" comes from - but that's really only true for water and things close to it.
Flour is the one genuinely disputed figure on this list, and it's worth taking seriously: how tightly you pack a cup of flour changes its weight by as much as 15-20%, which is enough to noticeably change a baked result. King Arthur Baking's own published testing → found spooning flour into the cup and leveling it gives about 120-125g, while scooping the cup directly into the bag and leveling gives 150-160g. Both methods above use the specific named standard from a real source rather than splitting the difference - match whichever your recipe's author actually used.