How Many Onions in a Cup – Your Guide to How Much Onion You Need

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If you love onions and love recipes that use them, you may find yourself scratching your head when a recipe calls for one cup of onions. It can be frustrating and difficult to figure out how many onions in a cup! In this article, we will explore ways you can determine how many onions are in one cup as well as how to approximate how many onions are in as many as 4 cups sliced.

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Cutting Onions

Is One Onion a Cup?

Among the many questions we often ask in the kitchen such as, What on earth is a baker’s gross?” and “Is all baking soda the same?”, the question that continues to stump many of us is how many onions make a cup.

The answer to, “Is one onion a cup?” is that it could be, but it depends on the size of the onion. 

There are onions that are small, medium-size, large, and very large. Thus, it is clear that onions of varying sizes will yield varying amounts.

Many have conducted tests to answer whether or not one onion equals one cup, and the consensus seems to be that one medium onion can yield anywhere from one to two cups. This is because what one might consider to be a “medium” onion another might consider to be small. 

For the sake of reference, a medium onion can be likened to the size of a navel orange. An onion this size will thus be expected to yield about one cup of chopped onion.

How Many Cups Is 3 Onions?

If we use the prior reference of one navel orange being equivalent in size to one medium-sized onion, we can then use a small red grapefruit as a reference for how big a large onion might be. 

Thus, using a red grapefruit as a size reference, you might expect a large onion of the same size to yield about 3 cups of onion for whatever dish you are preparing. Remember, this is only an approximation. You could end up with slightly more or slightly less onion than this amount, so be sure to leave room for error.

How Many Onions Is 1/2 Cup?

You will likely yield half a cup of onion from one small onion. 

In the previous sections, we likened a medium-sized onion to the size of a navel orange and a large onion to the size of a small red grapefruit. 

For this segment, we will liken a small onion to the size of your typical lemon. An onion this size will likely yield ½ cup of onions for your recipe – give or take.

How Many Onions Is 4 Cups Sliced?

When slicing onions, you’ll need to bear in mind that the coarseness of the slice, as well as the shape, will affect how many onions can fit in one cup. In fact, the more coarsely sliced your onion is, the more cups it will yield because those slices will take up more space than would a thinly sliced or diced onion. 

With this in mind, we can approximate that slicing a medium onion into strips that are about ½ inch thick could yield anywhere from double the number of cups it would if the onion had been diced. And because a medium onion will yield about one cup of diced onion, you might expect to get anywhere from 2-3 cups of onion when sliced.

How Many Cups Is a Large Onion?

One large onion can be likened to about 3 cups of onion, but that will depend on several factors. 

Assuming that the onions were diced and not sliced, you can expect to receive about 3 cups of onion from a large onion, but some will yield more or less. 

It really depends on what is meant by “large”.

For the purpose of this article, we consider a large onion to be the size of a small grapefruit. In this case, your onion may yield about three cups when chopped, and potentially 6 or more cups of onion when sliced, depending on the thickness of the slice.

How Many Cups Is One Large Onion?

One large onion offers about 3 cups of diced onion and even more cups of sliced onion. 

If you see a recipe that calls for one large onion, you can expect the recipe to have a strong onion flavor, which could be very delicious. Just note that it may take a while for you to dice this many onions. Slicing your onions, on the other hand, won’t take nearly as long. 

1 Medium Onion Equals How Many Cups?

One medium onion will deliver approximately 1 cup diced, but this is assuming that your onion is about the size of a navel orange. 

For some, an onion the size of a navel orange might seem quite large, so this is where things can get skewed. If one uses a smaller onion, a smaller portion can expect to be delivered, and thus, one might not end up with the exact amount of onions needed for the recipe. 

white and red onions

How Many Onions in a Cup Chopped

How Many Onions in a Cup Diced?

When chopping onions, it is important to keep in mind that the finer the dice, the more onion may appear to fill a cup. A quarter-inch dice of onion will likely yield the following result: 

Small OnionMedium OnionLarge Onion
1/2 Cup Diced1 Cup Diced3 Cups Diced

Of course, the above measurements are only approximate and will depend on the actual size of your onion. Since it’s all relative, you’ll want to make sure that you leave room for error by purchasing an extra onion or two, in case the amount you’ve chopped doesn’t yield enough for your dish.

How Much Is 1 Cup of Onions in Grams?

One cup of onion is the equivalent of 128 grams or 4.5 ounces. For exact measurements, consider using a kitchen scale

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It All Depends on Sizing…

Ultimately, how many onions make up a cup will depend on a variety of factors. These factors include the size of the onion and the way they are sliced. Typically, however, one medium onion will yield approximately one cup. Thus, if your recipe calls for one cup of diced onion, you should be safe purchasing a medium-sized onion that is about the size of a navel orange. 

Happy cooking!

By Anna

Hey, I’m Anna; writer, editor and amateur cook extraordinaire! Food has been my life and my passion for the most of my life – it’s crazy to think I didn’t pursue a career in cooking. I’m obsessed! However, keeping cooking as an obsessive hobby has worked for me – my passion grows as the years pass by – maybe I wouldn’t say the same if it was also my day job! I hope you find cooking inspiration, entertainment and “stop and think interesting tid-bits” throughout my writing – and I’d love to hear from you if you’ve got anything you want to share. Food feeds the soul – so get eating!

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