Volume vs weight

1-cup and 8-fluid-oz are related for the measure of liquids in USA (though many coffee makers and rice makers use a 6-fluid-oz cup standard)-- Imperial measurements for fluid-oz and "cups" is a bit different, but nothing to do with your question...

... the Fluid-Ounce (volume of liquid) and a scale ounce (measure of weight) are not meaningfully related.

For more fun, 21 CFR 101.9(b)(5)(viii) (United States) states that for nutritional labeling, a fluid ounce is exactly 30 milliliters, which is more like 1.0144 US fluid ounces (or 1.0559 imperial fluid ounces)...

...still -- not directly related to weight, though the original standard for fluid ounces (a volume measure) would have some origin in the weight of liquids (like water, wine, or ale).



Generally, if the recipe that you're working with (or label) specifically calls out a cup-volume-measure, that would most often refer to 8-FLUID-ounces (a volume measure) of whatever you're working with -- Aside from liquids, volumetric measurements are inherently inaccurate, which is why weight is preferred for accuracy. Basically, if you're forced to work in volume measurements then your stuck working in volumetric measurements... Unless you're calculating the density of the material in the measuring cup, you really can't convert that to an exact weight (e.g.: an 8-fluid-ounce cup of water will generally weigh a little more than 8.3 ounces on your scale -- and all bets are off for something like Cheerios or Spinach)

standenvernet wrote: »

... Unless you're calculating the density of the material in the measuring cup, you really can't convert that to an exact weight (e.g.: an 8-fluid-ounce cup of water will generally weigh a little more than 8.3 ounces on your scale -- and all bets are off for something like Cheerios or Spinach)

Just for the fun of it, I did some experiments in my kitchen weighing and measuring some foods ... and this is how it rolled for me ...
1 cup halved frozen strawberries weighed 5.3 oz
1 cup firmly packed baby spinach (as tight as I could make it) weighed 1 ounce.
1/4 cup ricotta cheese weighed 2.2 ounces

lynn_glenmont wrote: »

Nikion901 wrote: »

standenvernet wrote: »

... Unless you're calculating the density of the material in the measuring cup, you really can't convert that to an exact weight (e.g.: an 8-fluid-ounce cup of water will generally weigh a little more than 8.3 ounces on your scale -- and all bets are off for something like Cheerios or Spinach)

Just for the fun of it, I did some experiments in my kitchen weighing and measuring some foods ... and this is how it rolled for me ...
1 cup halved frozen strawberries weighed 5.3 oz
1 cup firmly packed baby spinach (as tight as I could make it) weighed 1 ounce.
1/4 cup ricotta cheese weighed 2.2 ounces

For all of those foods, the USDA nutrient database has entries based on weight, so there's really no need to do that. Plus, the whole point of using weight is that volume measurements won't be consistent -- one time, you'll get 5.3 oz of strawberries in a cup; another time you might 5.8 oz or 5 oz even.

Yea, I know this ...