Volume-to-Weight Converter
A cup of flour has no single weight, because how you fill the cup is part of the measurement. This converts volume to grams for 56 ingredients and names the fill method it assumed, shows you the range the published sources actually span, and declines the figures nobody has measured. The table and its sourcing are in Weights & Measures.
The ingredient
The amount
The weight
The eggs
Why the method is on the screen
Bulk density is not a constant of a powder. It is a property of how the powder was last handled, which is why the pharmaceutical standard for measuring it insists that any reported figure state how the determination was made. Wheat flour has a measured compressibility index between about 26 and 47 percent, meaning consolidated flour can approach twice the density of aerated flour. Plunging a cup through a bin applies exactly the consolidating stress that the laboratory tapped-density test applies deliberately, which is why dip-and-sweep runs 15 to 20 percent heavier than spoon-and-level, and why a cup filled from the settled bottom of a bag is heavier still.
So a converter that returns one number for a cup of flour has chosen a filling method silently. This one defaults to 120 g, the spooned-and-levelled figure, because that is the method the library's own articles assume and the one King Arthur recommends to anyone measuring by volume. Switch the method and the number moves to 125 g for the USDA figure, 142 g for dip-and-sweep, or 160 g for a packed cup, and the panel shows what every published source says so you can see the size of the disagreement rather than inherit a choice.
Liquids and fats are a different problem. Their cup weights are real densities, and two conventions in wide circulation are not: the treatment of a fluid ounce as an ounce of weight, which understates water, milk and cream by 4 to 8 percent, and a vegetable-oil figure of 198 g per cup, which works out to a density no edible oil has. This tool uses the measured figures and flags both. Butter is the opposite case, an honest convention rather than a measurement: its cup weight comes from the quarter-pound stick and the tablespoon marks printed on the wrapper, so it is exact at the printed lines and meaningless once the butter is melted.
Some figures are missing on purpose. There is no published cup weight for caster sugar, no source anywhere that gives cocoa both sifted and unsifted, no density curve for melted butter, and no kitchen figure for confectioner's glucose. Rather than interpolate, the ingredient list leaves them out and Weights & Measures says why.
The tables, the source reconciliation, and the gaps: Weights & Measures · Why weight makes a formula scalable: Ratios & Formula Frameworks · The scale, and the rest of the measuring kit: Tools & Equipment · Teaspoon weights for soda and powder: Chemical Leavening