Choosing the Right Onion Size: A Practical Guide for Cooking and Recipes

medium onion size

Have you ever found yourself perplexed by the concept of a medium onion while browsing through a recipe book? It can be quite a puzzle to determine the size of a medium onion when there is no standardized onion sizing system. Fortunately, the USDA has established guidelines for onion sizes, but if you’re short on time, I have a solution that can help.

Onions are typically categorized by weight or size. So, when we refer to a medium onion, we are talking about an onion that weighs between 6 and 8 ounces or measures approximately 3 to 3-3/4 inches in diameter.

To put that into perspective, a medium onion would weigh about the same as a roll of quarters or be roughly half the length of a dollar bill.

But there’s more to learn about onions, especially when it comes to cooking. In the following sections, I will provide you with all the relevant information you need to know about onion sizes to enhance your next culinary creation.

Understanding Onion Sizes

When you browse through the onion section at the grocery store, you might notice that all the onions in the crates or mesh bags seem to look the same. However, it’s important to know that onions are labeled based on their weight in ounces. Alternatively, you may choose to measure an onion based on its diameter.

By Weight

By categorizing onions according to weight, you can determine whether an onion is small, medium, or large. Here’s a quick overview of the weight ranges for each size category:

  • Small onions: 3 to 5 ounces
  • Medium onions: 6 to 8 ounces
  • Large onions: 10 to 12 ounces

It’s worth noting that these weight figures are averages, and the actual sizes of onions within a bag or crate may vary slightly. For example, a bag labeled as containing large onions, weighing around 5 pounds, may include 1 or 2 medium or small onions. However, the total weight of the bag will still be close to or precisely 5 pounds.

While I highly recommend using a reliable digital scale in your kitchen, you can also estimate the size of an onion by comparing it to everyday objects. A small onion would weigh approximately the same as 2 D-cell batteries, while a medium onion would weigh about the same as a roll of quarters. Lastly, a large onion would be similar in weight to a ceramic coffee mug. As for fruit equivalents, a small onion is about the size of a lemon, a medium onion is comparable to a navel orange, and a large onion is akin to a small grapefruit.

By Size

If you prefer a simpler way to determine the size category of an onion, you can measure its diameter. Now, I’m not suggesting you keep a ruler or tape measure handy every time you need to cook with onions. Instead, you can use common objects that have dimensions of around 3 or 4 inches.

With that in mind, let’s take a look at the size classifications of onions based on diameter. When onions are measured by size, they fall into one of six categories:

  • Creamer: Less than 1 inch in diameter
  • Small: 1 to 1-1/4 inches
  • Medium: 2 to 3-1/4 inches
  • Large: 3-1/4 to 3-3/4 inches
  • Colossal: 3-3/4 to 4-1/2 inches
  • Super Colossal: At least 4-1/2 inches

Using Onions in Recipes

Now that you understand the different sizes of onions, let’s explore how they look and feel when used in recipes.


Some recipes may not specify a small, medium, or large onion. Instead, they might provide volume measurements, usually in cups or teaspoons, for diced or chopped onions. So, how much onion should you use for each size category? While the results may vary, here are some approximate volume measurements for each size:

  • Small onion: 8 tablespoons or 1/2 cup
  • Medium onion: 16 tablespoons or 1 cup
  • Large onion: 24 tablespoons or 1.5 cups

Please keep in mind that the overall volume of a small, medium, or large onion can vary based on its weight. For example, a 3-ounce onion may yield approximately 1 or 2 tablespoons less minced onion compared to a 5-ounce onion, even though both fall into the small onion category.

The good news is that when a recipe calls for a specific onion size, you don’t have to worry about precise measurements. In most cases, adding or subtracting a few ounces of onions from a lunch or dinner recipe will not significantly impact the final outcome. If you’re planning to prepare minced, diced, or chopped onions, it’s best to stick with small, medium, or large onions. It’s advisable to avoid using colossal super colossal onions, as they may result in an excessive amount of onion compared to what the recipe requires.


If you’re preparing a recipe in larger quantities, the recipe may specify a certain weight of onions that need to be peeled and sliced. Without a digital scale, it may be challenging to measure the exact weight. However, understanding how many small, medium, or large onions make up a pound can be helpful.

In general, you can refer to the weight label on the mesh bag to determine the total weight of the onions. However, as mentioned earlier, a bag of onions may contain onions of various sizes that add up to the specified weight.

Let’s consider how many small, medium, and large onions would weigh approximately 1 pound:

  • Small onions: 3-2/5 to 5-1/3
  • Medium onions: 2 to 2-2/3
  • Large onions: 1-1/3 to 1-3/5

Remember, these are estimates, and the actual number of onions required to reach a pound may vary.

Understanding onion sizes can greatly assist you in selecting the right onion for your recipes. Whether you need a specific weight or size, you now have the knowledge to confidently choose the appropriate onion to enhance your culinary endeavors.