A kind of onion · also called Brown onion

2 views: its portrait, and how it looks in the comparison photos.
About
This sharp-flavored dry onion variety takes up about twice the volume of water when chopped into a cup.
Chopped yellow onion has a typical bulk density of about 4.2 ounces per cup (0.5 g/mL). The spaces between the diced pieces make it much lighter by volume than solid root vegetables like carrots or whole bulbs. Compared to finely minced garlic, chopped onion pieces pack loosely and leave larger pockets of empty air in a container.
From Wikipedia
The yellow onion or brown onion is a variety of dry onion with a strong flavor. It is yellow-white inside, with a brown, papery exterior.
Read more on Wikipedia →Text from Wikipedia’s “Yellow onion” article, CC BY-SA 4.0.
1 on the site
One cup weighs
4.17 oz (118 g)
Quick answer
One US cup of chopped yellow onion weighs about 4.2 ounces (118 g). That is roughly half the weight of a cup of water and about the same as one stick of butter.
Typical figures, the same ones every comparison on the site uses; real ones vary.
More like chopped yellow onion
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Next to anything: a person, a car, another onion.