Convert one ingredient at a time between volume and weight — cups, spoons, millilitres, grams and ounces — using the weight that ingredient actually has.
Volume-to-weight results depend on the ingredient selected. Spoon and cup measures are level measures.
Volume and weight only line up through an ingredient's density: a cup of flour weighs far less than a cup of honey. This converter first turns the starting amount into grams using the selected ingredient's standard cup weight, then turns those grams into the target unit. Results are rounded sensibly for kitchen use and work best with level spoon and cup measures, with dry ingredients spooned into the cup rather than scooped and packed — except brown sugar, which is listed packed.
Why does the ingredient matter? A cup measures space, not weight. Ingredients fill that space at different densities, so converting between cups and grams without naming the ingredient can be wrong by more than half.
How accurate are the cup weights? They use widely published standard cup weights. Real results vary a little with how an ingredient is measured, its brand and its humidity, so treat gram results as close kitchen values rather than laboratory figures.