Looking at the box is the most common way. A normal box of spaghetti pasta is usually a pound. Most recipes are referring to the dry weight, the weight before they are cooked.
A cup and an ounce measure different things. A cup is a measure of volume, while an ounce is a measure of weight. Generally speaking, dry spaghetti (or most any dry pasta) will double in size when you cook it. I'd estimate that if you cook 2 ounces of dry spaghetti, you will get roughly one cup cooked spaghetti.
A serving size of spaghetti is considered to be 1/4 to 1/2 cup. Since you can not measure spaghetti in a measuring cup let's switch to ounces. 1/4 of a cup of dry spaghetti is 2 ounces, once cooked it measures about 4.5 ounces. So to get enough cooked spaghetti for 1 serving per person, for 20 people you need 20 about 20 ounces of dry spaghetti, or 1.25 lbs. 1.25 lbs of dry spaghetti will cook into approximately 2.8 lbs of cooked spaghetti, which is 45 ounces. 45 ounces which is roughly 5.6 cups, and 5.6 cups divided into 1/4th cup servings of cooked spaghetti gives you about 22 servings. If you feel people are going to want more than 1 serving then cook up another half pound of spaghetti to be safe.
7 fluid ounces approx. = 22 one hundredths of a gallon
You must name the pasta, there are dozens of kinds and all weigh different. For example, a cup of spaghetti,all standing upright and closely fitted in a cup is 3 times the weight of rotini
Four ounces of dry spaghetti will make two cups when cooked.
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It is a weight measure. Ounces is weight.
Inches
896 oz 1 gallon makes 128 ounces and 1 ounce is 0.0078 gallon in U.S measure. There are 8 ounces in a cup, 2 cups in a pint, 2 pints in a quart and 4 quarts in a gallon. That makes 128 ounces in a gallon US. In UK 20 ounces to the pint, 8 pints to the gallon which makes 160 ounces Imperial measure.
14.5 ounces of angel hair ..when cooked 2 lbs 8 ounces...