Quick Answer
A medium onion is approximately 1/2 to 3/4 cup chopped. The exact amount can vary depending on the size and variety of the onion. On average, one medium onion yields about 1/2 cup when chopped.
Calculating Onion Cup Measurements
When a recipe calls for a certain cup measurement of onion, it’s helpful to know how much onion you need to purchase and prepare. Here are some guidelines for onion cup conversions:
Medium Onion
– Whole: 1 medium onion
– Chopped: 1/2 to 3/4 cup
– Diced: 1/2 to 2/3 cup
– Sliced: 1/2 to 3/4 cup
Large Onion
– Whole: 1 large onion
– Chopped: 3/4 to 1 cup
– Diced: 2/3 to 1 cup
– Sliced: 3/4 to 1 cup
Small Onion
– Whole: 1 small onion
– Chopped: 1/3 to 1/2 cup
– Diced: 1/3 cup
– Sliced: 1/3 to 1/2 cup
The size of the pieces (chopped vs. diced vs. sliced) makes a difference in the cup measurements. More finely diced or sliced onions will pack down more in the measuring cup.
When in doubt, it’s best to err on the side of using more onion. Extra onion can always be saved for another use. Too little onion can ruin the flavor of a dish.
Onion Varieties
Different onion varieties vary in size, which affects their cup measurements. Here are some common varieties and their approximate cup amounts when chopped:
Yellow Onion
– Small: 1/3 cup
– Medium: 1/2 cup
– Large: 3/4 cup
– Extra Large: 1 cup
Red Onion
– Small: 1/3 cup
– Medium: 1/2 cup
– Large: 2/3 cup
White Onion
– Small: 1/3 cup
– Medium: 1/2 cup
– Large: 3/4 cup
Sweet Onion
– Small: 1/3 cup
– Medium: 1/2 to 2/3 cup
– Large: 3/4 to 1 cup
Sweet onions like Vidalia and Walla Walla tend to run larger than other varieties.
Shallots
– Small/Medium: 2 to 3 tablespoons chopped
– Large: 1/4 cup chopped
Shallots are smaller than regular onions, so you need less for the same onion flavor.
Leeks
– Small: 1/4 cup chopped
– Medium: 1/3 cup chopped
– Large: 1/2 cup chopped
Leeks look like oversized scallions. When chopped, they yield about 1/4 to 1/2 cup per leek.
Scallions (Green Onions)
– Bunch: 1/4 to 1/3 cup chopped
Scallions are the smallest onion variety. A bunch usually provides around 1/4 cup chopped.
Weight Measurements
Onions can also be measured by weight instead of volume. Here are the approximate weights of different sized onions:
Small Onion
– 3 to 5 ounces
Medium Onion
– 5 to 7 ounces
Large Onion
– 7 to 10 ounces
Extra Large Onion
– 10 to 12 ounces
In general, 1 medium onion is approximately 5 to 7 ounces by weight.
Cup Conversions
Here is a table summarizing the approximate cup measurements for different sizes and types of onions:
| Onion Variety and Size | Chopped | Diced | Sliced |
|---|---|---|---|
| Small Yellow Onion | 1/3 cup | 1/3 cup | 1/3 cup |
| Medium Yellow Onion | 1/2 cup | 1/2 cup | 1/2 cup |
| Large Yellow Onion | 3/4 cup | 2/3 cup | 3/4 cup |
| Extra Large Yellow Onion | 1 cup | 1 cup | 1 cup |
| Small Red Onion | 1/3 cup | 1/3 cup | 1/3 cup |
| Medium Red Onion | 1/2 cup | 1/2 cup | 1/2 cup |
| Large Red Onion | 2/3 cup | 2/3 cup | 2/3 cup |
| Small White Onion | 1/3 cup | 1/3 cup | 1/3 cup |
| Medium White Onion | 1/2 cup | 1/2 cup | 1/2 cup |
| Large White Onion | 3/4 cup | 3/4 cup | 3/4 cup |
| Small Sweet Onion | 1/3 cup | 1/3 cup | 1/3 cup |
| Medium Sweet Onion | 1/2 to 2/3 cup | 1/2 to 2/3 cup | 1/2 to 2/3 cup |
| Large Sweet Onion | 3/4 to 1 cup | 3/4 to 1 cup | 3/4 to 1 cup |
| Small/Medium Shallots | 2 to 3 Tbsp | 2 to 3 Tbsp | 2 to 3 Tbsp |
| Large Shallots | 1/4 cup | 1/4 cup | 1/4 cup |
| Small Leek | 1/4 cup | 1/4 cup | 1/4 cup |
| Medium Leek | 1/3 cup | 1/3 cup | 1/3 cup |
| Large Leek | 1/2 cup | 1/2 cup | 1/2 cup |
| Bunch Scallions | 1/4 to 1/3 cup | 1/4 to 1/3 cup | 1/4 to 1/3 cup |
Tips for Measuring Onions
– When chopping onions, aim for approximately 1/2-inch pieces. Finely diced onions should be about 1/4-inch.
– For sliced onions, cut on the bias for longer oval shaped pieces rather than small circles.
– Before chopping or slicing, peel off the papery outer layer of skin. Leave the root end intact for easy handling.
– Rinse onions and pat dry to remove any dirt or debris before cutting. Wet onions won’t pack properly into measuring cups.
– When measuring chopped, diced, or sliced onions, lightly pack the pieces into the cup without compressing too much.
– For recipes that use a lot of onions, consider weighing for the most accuracy. You can then measure out portions by weight instead of volume.
– Onions can vary in moisture content, which affects measurements. If an onion seems moist and heavy, err on the side of using a bit more than the recipe calls for to account for any extra moisture.
– Store unused chopped onions in an airtight container in the refrigerator for 3-4 days. They lose flavor and moisture quickly once cut.
– If a recipe calls for 1/2 medium onion, use 1/4 to 1/3 cup chopped onion. For 3/4 medium onion, use 1/3 to 1/2 cup chopped onion based on the equivalents above.
What About Green Onions and Shallots?
Green onions and shallots are smaller onion varieties that are measured a bit differently:
Green Onions
– Also known as scallions or spring onions
– Sold in bunches
– Entire green onion is used, including white bulb and green stalks
– A bunch usually provides around 1/4 to 1/3 cup chopped
Shallots
– Look like small bulbs sort of a cross between garlic and onions
– Milder in flavor than onions
– Most recipes call for 2-3 tablespoons chopped shallots instead of onions
– An average shallot yields around 2 tablespoons chopped
– Large shallots may provide up to 1/4 cup chopped
So for green onions and shallots, the bunch or quantity needed depends on the recipe and amount of flavor desired. Start with less and add more as needed. Their milder flavor means you typically use less volume than regular onions.
Onion Measurement Substitutions
In a pinch, here are some handy substitution equivalents:
– 1 medium onion = 1/4 cup dehydrated onion flakes or 1 tablespoon onion powder (rehydrate in a little water first for onion flakes)
– 1/2 medium onion = 2 tablespoons dried minced onion
– 1/2 medium onion = 1 teaspoon onion extract or essence
Dehydrated, dried, or concentrated onion products make suitable substitutes, but onions lose some of their aromatic flavor compounds when dried. Use a bit more than the equivalent fresh onion measurement for best results.
Common Onion Amounts in Recipes
Here are typical onion amounts called for in recipes:
– Soups, stews, chili: 1 to 2 medium onions chopped (1/2 to 1 cup)
– Salad dressings, marinades: 1/4 to 1/2 medium onion chopped (1/4 to 1/3 cup)
– Burgers, meatloaf, meatballs: 1/4 to 1/2 onion minced or grated
– Stir fries: 1 medium onion sliced or 1 bunch green onions
– Fajitas, tacos: 1/2 medium onion sliced or diced
– Omelets, quiches, stratas: 1/4 to 1/2 onion diced or sliced
– Casseroles, pasta bakes: 1 medium onion chopped
– Caramelized onions: 2 to 3 medium onions sliced
– French onion soup: 2 to 3 medium onions sliced
– Guacamole: 1/4 to 1/2 medium onion diced
– Pasta sauce: 1/2 to 1 medium onion diced
– Pizza: 1/4 to 1/2 medium onion sliced or diced
– Roasted vegetables: 1 medium onion cut into wedges
– Quesadillas: 1/4 medium onion diced or sliced
– Sandwiches, wraps: 1 to 2 tablespoons minced onion
Typical Medium Onion Weights
The weight of a medium onion can vary somewhat based on the specific type and size. But in general, a medium onion weighs:
– Medium Yellow Onion: Approximately 5 to 7 ounces
– Medium Red Onion: Approximately 4 to 6 ounces
– Medium White Onion: Approximately 6 to 8 ounces
– Medium Sweet Onion: Approximately 6 to 8 ounces
For shallots, a medium shallot is usually around 1.5 to 2 ounces.
How Much Is 1 Cup of Onion?
Since most medium onions yield around 1/2 to 3/4 cups chopped, 1 cup of chopped onion is equivalent to:
– 1 to 2 medium yellow, red, or white onions
– 1 large yellow, red, or white onion
– 1 extra large sweet onion like Vidalia or Walla Walla
– 2 medium leeks
– 1 small head of fennel
– 1 large shallot or 5-6 medium shallots
– 1 tablespoon onion powder plus 1/4 cup water
– 1/4 cup dried onion flakes plus 1/4 cup water
Storing Onions
Properly stored, whole onions will keep for 1-2 months at room temperature. Once cut, onions only last 3-4 days in the refrigerator before they start to spoil. To maximize freshness:
– Store whole, unpeeled onions in a cool, dry, ventilated place away from sunlight. A basket or mesh bag works better than a sealed container.
– Avoid refrigerating whole raw onions—the cold breaks down their pungent flavors.
– Cut onions dulled kitchen knives. A blunt edge crushes the cells rather than slicing cleanly, accelerating deterioration.
– Place chopped, sliced, or diced onions in an airtight container or resealable plastic bag. Make sure onions are completely dry before storing them.
– You can also freeze diced or sliced onions for longer storage. Portion onions into freezer bags or containers, removing as much air as possible. They’ll keep for 3-6 months in the freezer.
Onion Measurement FAQs
Get answers to some common questions about measuring onions:
How much onion equals a tablespoon?
One tablespoon of minced onion is approximately one quarter of a small onion or one eighth of a medium onion.
Can you use onion powder instead of an onion?
Yes, substitute 1 teaspoon of onion powder for 1/2 a medium onion. Rehydrate the onion powder in a little water first before adding to the dish.
Is a shallot the same as a small onion?
Shallots are actually a separate onion variety, botanically speaking. Unlike regular bulbing onions, shallots grow in clusters somewhat like garlic. While they look like very small onions, they have a milder, sweeter flavor.
How long does an open onion last in the refrigerator?
Chopped raw onions will last 3-4 days when properly stored in an airtight container in the fridge. Cooked onions will last 4-5 days refrigerated. Discard onions if they become overly soft or slimy.
Can you freeze an onion?
Yes, you can dice, slice, or grate raw onions then freeze them in airtight bags or containers. Frozen onions are best used for cooking rather than eating raw.
Conclusion
Estimating onion measurements is an important kitchen skill for following recipes accurately. With the cup conversions, guidelines, and tips above, you should feel confident measuring out the right onion amount for whatever dish you’re preparing. As with any vegetable, onion sizes can vary, so taste and adjust the flavor as needed. Let your taste buds be the final judge on whether you have just the right amount of onion.
