The quick rule: 1 medium onion = about 1 cup chopped = 4–5 oz / 113–142g.
Onion Conversion Calculator
Convert whole onions or weight into approximate chopped and sliced amounts.
One medium onion is about 4–5 ounces before peeling.
Keep in mind: Onion sizes overlap, and volume changes with the cut and how tightly you fill the cup. These are close kitchen estimates. Weigh the peeled onion when precision matters.
Fast Onion Conversion Guide
Quick answer: One medium onion weighs about 4–5 ounces and yields about ½–¾ cup chopped or ¾–1 cup thinly sliced.
- 1 small onion = about 3 ounces = ⅓–½ cup chopped
- 1 medium onion = about 4–5 ounces = ½–¾ cup chopped
- 1 large onion = about 8 ounces = 1–1¼ cups chopped
- 3 medium onions = approximately 1 pound
- 2 large onions = approximately 1 pound
- 1 pound whole onions = about 2–2½ cups chopped
- Thinly sliced onions take up more measuring-cup space than chopped onions.
Onion size, trimming, cut size and how tightly you fill the measuring cup can all change the final amount.
What Counts as a Small, Medium or Large Onion?
Onion size names describe a general range, not an exact weight. For this guide, we use the following practical kitchen measurements:
- A small onion weighs about 3 ounces (85 grams).
- A medium onion weighs about 4–5 ounces (110–140 grams).
- A large onion weighs about 8 ounces (225 grams).
When possible, measure the onion across its widest point or weigh it before cutting. A typical medium onion measures approximately 2½ inches across, while a large onion usually measures at least 3 inches across.
Onion Conversion and Yield Chart
Use these estimates to convert whole onions into chopped or thinly sliced onion.
| Whole Onion Amount | Approximate Weight | Chopped Yield | Thinly Sliced Yield |
|---|---|---|---|
| ½ small onion | 1½ oz / 43 g | About ¼ cup | About ⅓ cup |
| 1 small onion | About 3 oz / 85 g | ⅓–½ cup | ½–¾ cup |
| ½ medium onion | About 2¼ oz / 64 g | About ⅓ cup | About ½ cup |
| 1 medium onion | 4–5 oz / 110–140 g | ½–¾ cup | ¾–1 cup |
| ½ large onion | About 4 oz / 113 g | ½–⅔ cup | ¾–1 cup |
| 1 large onion | About 8 oz / 225 g | 1–1¼ cups | 1½–2 cups |
| 3 medium onions | About 1 lb / 454 g | 2–2½ cups | About 3 cups |
| 2 large onions | About 1 lb / 454 g | 2–2½ cups | About 3–4 cups |
| 1 lb whole onions | 16 oz / 454 g | 2–2½ cups | About 3–3½ cups |
Size guide: A small onion is about 3 ounces, a medium onion is about 4–5 ounces, and a large onion is about 8 ounces. Yields vary with the onion's shape, the amount trimmed, the cut size and how tightly you fill the measuring cup.
Fresh Onion to Dried Onion Conversion Chart
Use these amounts when replacing chopped fresh onion with dried minced onion or onion powder.
| Fresh Onion Amount | Dried Minced Onion | Onion Powder |
|---|---|---|
| ¼ cup chopped fresh onion | About 1½ tablespoons | 1–1½ teaspoons |
| ½ cup chopped fresh onion | About 3 tablespoons | 2–3 teaspoons |
| ¾ cup chopped fresh onion | About 4½ tablespoons | 3–4½ teaspoons |
| 1 cup chopped fresh onion | About 6 tablespoons | 4–6 teaspoons |
| 1 small onion ⅓–½ cup chopped |
2–3 tablespoons | 1½–2½ teaspoons |
| 1 medium onion ½–¾ cup chopped |
3–4½ tablespoons | 2–4 teaspoons |
| 1 large onion 1–1¼ cups chopped |
6–7½ tablespoons | 4–6 teaspoons |
For onion powder: Start with the lower amount, cook or let the mixture rest, then taste before adding more. Powder strength varies by brand and age.
For dried minced onion: Add it directly to soups, stews and other dishes with enough liquid. For dry or quick-cooking dishes, rehydrate it according to the package directions before adding it.
Texture matters: Dried minced onion can replace some of the body of chopped onion. Onion powder supplies flavor but does not replace the moisture, texture or bulk of fresh onion.
Do Yellow, White, Red and Sweet Onions Convert Differently?
Yellow, white, red and sweet onions use the same basic weight-to-volume conversions. Variety matters less than the onion’s actual size and shape.
Sweet onions are often wider and flatter than storage onions, while red onions may have thicker outer layers that require more trimming. Those differences can slightly change the usable amount, but not enough to require separate conversion tables. Weigh the peeled onion when an exact amount matters.
What Cooks Get Wrong When Converting Onions
The biggest mistake is treating small, medium and large onions as exact measurements. They aren’t. Commercial onion-size categories overlap, and onions sold individually at the supermarket may be much larger than those packed in a bag.
Cooks also assume that one medium onion always equals one cup chopped. Some conversion guides use that shortcut, but a typical 4- to 5-ounce onion usually produces closer to ½–¾ cup after peeling and trimming. A particularly large “medium” onion may come closer to one cup.
The cut matters too. Thin slices form loose layers and take up more room in a measuring cup. Chopped onion packs more closely, while finely minced onion packs tighter still. One onion can therefore produce different cup measurements without changing the amount of onion.
Finally, an onion loses some weight when you remove its skin, stem, root and damaged outer layers. If a recipe requires an exact amount, weigh the onion after peeling and trimming. For everyday cooking, the ranges in the calculator and chart will get you close enough.
Frequently Asked Questions About Onion Conversions
What size onion equals 1 cup chopped?
One medium onion yields about 1 cup of chopped onion. A large onion yields about 1½ cups and a small onion yields about ½ cup.
How many onions do I need for 2 cups chopped?
Two medium onions yield about 2 cups chopped — or one large onion if it runs on the bigger side.
What can I use instead of ½ cup chopped onion?
½ teaspoon onion powder or 1 tablespoon dried minced onion. Both work well in cooked dishes — onion powder blends in completely, dried minced onion holds a little texture.
How much dried onion equals ¼ cup fresh chopped onion?
1 tablespoon of dried minced onion equals about ¼ cup of fresh chopped onion.
How much onion powder equals one medium onion?
About 1 teaspoon of onion powder replaces one medium onion. Onion powder is concentrated — start with less and adjust.
How much onion powder equals 1 cup of chopped onion?
About 1 tablespoon of onion powder equals 1 cup of fresh chopped onion.
How much do onions shrink when cooked?
Raw onions lose roughly 30–40% of their volume when sautéed and up to 75% when caramelized. 2 cups of raw sliced onion yields about ½ cup of caramelized onion.
How many onions do I need to make 1 cup of caramelized onions?
Plan on 3 to 4 medium onions per cup of caramelized onions — they shrink dramatically during the long cook.
How much does a medium onion weigh?
A medium onion weighs about 4–5 ounces (113–142 grams) before peeling. After peeling you lose about half an ounce.
Can I substitute frozen onions for fresh onions?
Yes, at a 1:1 ratio by volume — frozen onions are pre-chopped and release more water when cooked, so they work best in soups, stews, and braises rather than sautés where you want browning.