Quick Answer
3/4 cup equals approximately 177 grams of water.
For common kitchen ingredients, 3/4 cup is about 94 grams of all-purpose flour, 150 grams of granulated sugar, 165 grams of packed brown sugar, 170 grams of butter, and 139 grams of uncooked white rice.
The exact gram amount changes by ingredient because cups measure volume and grams measure weight.