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Onion Nutrition & Calories – Complete Data of All Nutrients

Onions, raw
*all the values are displayed for the amount of 100 grams
Article author photo Victoria Mazmanyan by Victoria Mazmanyan | Last updated on September 27, 2023
Medically reviewed by Arpi Gasparyan Article author photo Arpi Gasparyan


While onions are not exceptionally high in most macronutrients, they can be an excellent source of phytochemicals that provide an array of beneficial effects on human health.

Most of the macronutrient content of onions is composed of carbohydrates and a smaller amount of protein. Onions can also be a good source of vitamin B6 and vitamin C.


Onions are one of the most commonly used vegetables around the world. They are famous for their flavorful taste, pungent smell, and eye-irritating qualities. However, the nutrition of onions is often left out of the conversation. 

In this article, we will discuss every detail of the nutritional content of onions: macro and micronutrients, phytochemicals, nutritional differences in onion parts and varieties, and the influence of cooking.


The nutritional information below is presented for 100g of raw onions. We will also separately compare the nutrition of specific types of onions.

One average serving of onions per person is one tablespoon of chopped onions, equal to 10g.

Onions are not very dense in nutrients, consisting of 87% water and only 13% nutrients.

Macronutrients chart

2% 10% 87%
Daily Value: 2%
1.1 g of 50 g
Daily Value: 0%
0.1 g of 65 g
Daily Value: 3%
9.34 g of 300 g
Daily Value: 4%
89.11 g of 2,000 g
0.35 g


A 100g serving of raw onions provides 40 calories. Consequently, one average serving size of onions provide 4 calories.

What Does 40 Calories or 100 Grams of Onion Look Like?

We measured what 100 grams of onion looks like to help you visualize its weight and calories. As evident in the picture, approximately half of a medium-sized onion accounted for the entire 100 grams or 40-44 calories. This implies that a typical onion weighs about 145 grams and contains approximately 58 calories. Keep in mind that the actual weight and calorie content may vary depending on the size of the onion.

40 Calories or 100 Grams of Onion


Onions are not exceptionally high in proteins, containing only 1.1g of protein in a 100g serving.

Proteins found in onions include low levels of all essential amino acids except for methionine, which is absent in this vegetable. Onions are comparably higher in tryptophan.

Protein quality breakdown

Tryptophan Threonine Isoleucine Leucine Lysine Methionine Phenylalanine Valine Histidine 15% 6% 3% 3% 6% 1% 5% 4% 6%
Tryptophan: 14 mg of 280 mg 5%
Threonine: 21 mg of 1,050 mg 2%
Isoleucine: 14 mg of 1,400 mg 1%
Leucine: 25 mg of 2,730 mg 1%
Lysine: 39 mg of 2,100 mg 2%
Methionine: 2 mg of 1,050 mg 0%
Phenylalanine: 25 mg of 1,750 mg 1%
Valine: 21 mg of 1,820 mg 1%
Histidine: 14 mg of 700 mg 2%


Among macronutrient content, carbohydrates are found in the highest amounts in onions.

A hundred gram serving of onions provides 9.34g of carbohydrates.

Net Carbs

Most of the onion's carbohydrates consist of net carbs. A 100g of raw onions provides 7.64g of net carbs, 55% of which are sugars.

The predominant sugar in onions is glucose (1.97g), followed by fructose (1.29g) and sucrose (0.99g). Onions are naturally absent in starch and lactose.

Carbohydrate type breakdown

23% 46% 30%
Starch: 0 g
Sucrose: 0.99 g
Glucose: 1.97 g
Fructose: 1.29 g
Lactose: 0 g
Maltose: 0 g
Galactose: 0 g

In a comparison between different varieties of onions, one study found white onions from the US contain over 3 times more sugar than red onions from Egypt (1).

Dietary Fiber

In a 100g serving, onions contain 1.7g of fiber. Of this fiber content, 37% consists of soluble fiber, and 63% consists of insoluble fiber (2). 

Insoluble fiber helps the food pass more quickly and relieves constipation, whereas soluble fiber may aid in decreased blood cholesterol and glucose levels. 

Fiber content ratio for Onion

45% 18% 36%
Sugar: 4.24 g
Fiber: 1.7 g
Other: 3.4 g

Below is a carbohydrate content comparison between four onion varieties (3, 4, 5, 6).

VarietyCarbohydratesNet carbsSugarsDietary fiber
Red onion9.9g7.7g5.76g2.2g
White onion7.7g6.5g5.76g1.2g
Yellow onion8.6g6.7g5.82g1.9g
Green onion5.7g3.9g3.91g1.8g


Onion, along with garlic, legumes, and wheat products, is a frequently consumed high-FODMAP food. 

FODMAPs (fermentable oligosaccharides, disaccharides, monosaccharides, and polyols) are sugars poorly absorbed in the small intestines and mainly fermented by the colonic bacteria. 

FODMAPs are safe for most people; however, they are best avoided for people with gastrointestinal diseases, such as IBS, functional abdominal distension, functional diarrhea, functional constipation, Crohn's disease, and ulcerative colitis, as they may trigger or worsen the symptoms (7, 8). Due to high FODMAPs, onions may also cause heartburn in some people.


Onions contain a negligible amount of fats - around 0.1g per every 100g serving.

Fat type information

58% 18% 24%
Saturated Fat: 0.042 g
Monounsaturated Fat: 0.013 g
Polyunsaturated fat: 0.017 g


Onions are a good source of vitamin C, falling in the top 27% of foods as a source of vitamin C. However, a 100g serving covers only 8% of the daily needed amount of vitamin C.

The same serving size of onions can also cover 9% of the daily needed vitamin B6 content.

Onions are relatively high in vitamin B9, also known as folate.

This vegetable contains moderate-to-low levels of vitamins A, K, and E and B1, B2, B3, and B5.

Onions are absent in vitamin D and vitamin B12.

Vitamin coverage chart

Vitamin A Vitamin E Vitamin D Vitamin C Vitamin B1 Vitamin B2 Vitamin B3 Vitamin B5 Vitamin B6 Folate Vitamin B12 Vitamin K 1% 1% 0% 25% 12% 7% 3% 8% 28% 15% 0% 1%
Vitamin A: 2 IU of 5,000 IU 0%
Vitamin E : 0.02 mg of 15 mg 0%
Vitamin D: 0 µg of 10 µg 0%
Vitamin C: 7.4 mg of 90 mg 8%
Vitamin B1: 0.046 mg of 1 mg 4%
Vitamin B2: 0.027 mg of 1 mg 2%
Vitamin B3: 0.116 mg of 16 mg 1%
Vitamin B5: 0.123 mg of 5 mg 2%
Vitamin B6: 0.12 mg of 1 mg 9%
Folate: 19 µg of 400 µg 5%
Vitamin B12: 0 µg of 2 µg 0%
Vitamin K: 0.4 µg of 120 µg 0%


Onions provide some levels of most essential minerals. They are relatively rich in calcium, manganese, and potassium.

These vegetables contain low amounts of magnesium, phosphorus, copper, zinc, iron, selenium, and choline.


Onions naturally contain only 4mg of sodium per 100g serving.

Mineral coverage chart

Calcium Iron Magnesium Phosphorus Potassium Sodium Zinc Copper Manganese Selenium Choline 7% 8% 8% 13% 13% 1% 5% 14% 17% 3% 4%
Calcium: 23 mg of 1,000 mg 2%
Iron: 0.21 mg of 8 mg 3%
Magnesium: 10 mg of 420 mg 2%
Phosphorus: 29 mg of 700 mg 4%
Potassium: 146 mg of 3,400 mg 4%
Sodium: 4 mg of 2,300 mg 0%
Zinc: 0.17 mg of 11 mg 2%
Copper: 0.039 mg of 1 mg 4%
Manganese: 0.129 mg of 2 mg 6%
Selenium: 0.5 µg of 55 µg 1%
Choline: 6.1 mg of 550 mg 1%


Oxalates or oxalic acids are compounds in various vegetables, fruits, grains, and nuts. They are safe to consume for most people; however, they may increase the risk of some people developing calcium oxalate kidney stones.

Onion contains 5mg of oxalates per 100g, making it a low-oxalate food.


As plants, onions are abundant in health-beneficial phytonutrients that do not fall under the previously mentioned categories.

The onion species are known to contain many secondary metabolites, such as flavonoids, phytosterols, saponins, and anthocyanins (9, 1).

Potentially, the most significant importance of phytochemical compounds is their antioxidant capability, which reduces cell damage in the body by inhibiting lipid oxidation.

Due to these and various other compounds, onions have expressed anticancer, antidiabetic, antioxidant, antiplatelet, antihypertensive, antidepressant, neuroprotective, anti-inflammatory, antiparasitic effects, and more (10).


Isoalliin is a major sulfur-containing component of onions, which gives this vegetable its specific taste and eye-irritating quality (11). This compound is named after the scientific name of onions - Allium cepa.


Flavonoids are potent antioxidants from the polyphenol family of phytochemicals. Onions are considered an incredible source of flavonoids. In particular, onions are rich in quercetin, kaempferol, and isorhamnetin (11).

Red onions are usually richer in flavonoids than yellow and white varieties. However, the growing conditions and storage duration influence the flavonoid content (12).


Anthocyanins are also antioxidants from the phenolic group. These compounds are pigments responsible for fruits and vegetables' red, blue, and purple colorings. Therefore, red onions are considerably richer in anthocyanins than white onions (1).


Saponins are bitter-tasting compounds found in many fruits and vegetables, including onions. This phytochemical has been proven to reduce cholesterol absorption from the intestines. Saponins have also been studied to have antifungal and antitumor qualities (13).

Nutritional Differences Between Different Types of Onions

In this section, we will look at how the nutritional contents differ based on the variety of onions. The information is presented for 100g servings of raw red, white, and yellow onions (3, 4, 5).

Variety (raw)WaterCalorieFatsProtein
Red onion88.6g44kcal0.1g0.9g
White onion91.2g36kcal0.13g0.9g
Yellow onion90.1g38kcal0.05g0.8g

Red onions are slightly richer in magnesium, phosphorus, potassium, copper, and manganese, yellow onions are richer in calcium and zinc, and white onions are slightly richer in iron.

Nutritional Differences Between Onion Bulb & Green Tops

In this section, we'll compare onion bulbs to the young green tops and see which is nutritionally superior (6).

A 100g serving of onion bulbs contains 3.5g more carbohydrates; interestingly, the bulb and green tops contain almost equal amounts of dietary fiber. Onion bulb is slightly higher in protein, whereas green tops are slightly higher in fats.

Green tops are rich in vitamin A and carotenoids (terpenoid phytochemicals) called lutein and zeaxanthin, which are nearly absent in bulbs. 

Vitamin A is essential for vision, the immune system, organ development, and more; its deficiency commonly causes dry eyes and, in severe cases, night blindness. Carotenoids are also essential for vision, as they filter blue light and reduce the formation of harmful free radicals (14, 15).

A 100g of the tops also contains 156mcg of vitamin K, required for blood clotting (16).

Green tops of onions are also slightly richer in minerals, vitamins B3, C, A, E, K, and folate. On the other hand, onion bulbs are slightly richer in vitamins B1, B6, and choline.

Glycemic Index

An exact number for the glycemic index value of onions has not been calculated, but it is assumed to be low.

Raw onion has been researched to lead to reduced blood glucose concentration and body weight gain (17).

Freeze-dried onion powder has been studied to be protective against hyperglycemia (high blood sugar) and dyslipidemia (imbalance of blood fats) arising from diabetes in animal studies (18).

Onion powder has also been demonstrated to decrease the glycemic index of the pasta supplemented with (19).


The acidity of onions has been calculated to fall in the range of 6.2 (Baby variety) to 6.4 (Leek variety). Yellow, green, and red onions have a pH value of about 6.3 (20). 

However, onions' potential renal acid load or PRAL value is -2, proving onions to be alkaline-forming or base-producing inside the body.

Cooking Methods on Phytochemical and Nutritional Changes

Cooking methods such as baking, boiling, frying, and grilling affect the phytochemical content and bioavailability. 

Baking and grilling make the phenolic compounds' bioaccessibility the greatest compared to other cooking methods, or, in simple words, baking and grilling onions make the polyphenols more accessible for digestion and absorption in the intestines. However, cooking for extended periods may cause degradation or loss of some polyphenols (21).

During cooking, vitamin C, B-complex vitamins, and several minerals may be reduced due to being leached into the cooking water or destroyed by heat (22).

Cooking onions at a lower temperature for a short period and without draining the water may be the preferred choice to keep them nutritious.

Comparison to Similar Foods

This section will compare onions with similar vegetables, namely chives, garlic, and leek.

Onions are richer in calories and net carbs than chives, while chives are richer in dietary fiber and 3 times higher in protein. Chives also contain appreciably more extensive amounts of minerals and vitamins.

Between garlic and onion, garlic is significantly higher in calories, protein, and carbohydrates, including net carbs and dietary fiber. Garlic is also richer in most vitamins, except for folate. However, it is essential to note that the average serving size of garlic is about 4 times smaller than onions.

Leeks are slightly higher in calories, protein, carbohydrates, and vitamins than garlic.

Important nutritional characteristics for Onion

Glycemic index ⓘ Gi values are taken from various scientific sources. GI values less than 55 are considered as low. Values above 70 are considered as high. 15 (low)
Calories ⓘ Calories per 100-gram serving 40
Net Carbs ⓘ Net Carbs = Total Carbohydrates – Fiber – Sugar Alcohols 7.64 grams
Serving Size ⓘ Serving sizes are taken from FDA's Reference Amounts Customarily Consumed (RACCs) 1 tbsp chopped (10 grams)
Acidity (Based on PRAL) ⓘ PRAL (Potential renal acid load) is calculated using a formula. On the PRAL scale the higher the positive value, the more is the acidifying effect on the body. The lower the negative value, the higher the alkalinity of the food. 0 is neutral. -2 (alkaline)
Oxalates ⓘ 5mg
TOP 27% Vitamin C ⓘHigher in Vitamin C content than 73% of foods
TOP 40% Fiber ⓘHigher in Fiber content than 60% of foods
TOP 44% Folate, food ⓘHigher in Folate, food content than 56% of foods
TOP 49% Folate ⓘHigher in Folate content than 51% of foods
TOP 50% Sugar ⓘHigher in Sugar content than 50% of foods

Onion calories (kcal)

Serving Size Calories Weight
Calories in 100 grams 40
Calories in 1 cup, chopped 64 160 g
Calories in 10 rings 24 60 g
Calories in 1 cup, sliced 46 115 g
Calories in 1 tbsp chopped 4 10 g
Calories in 1 large 60 150 g
Calories in 1 small 28 70 g
Calories in 1 slice, thin 4 9 g

Onion Glycemic index (GI)

Gi values are taken from various scientific sources. GI values less than 55 are considered as low. Values above 70 are considered as high.

Mineral chart - relative view

23 mg
TOP 50%
0.129 mg
TOP 58%
146 mg
TOP 71%
10 mg
TOP 84%
29 mg
TOP 84%
0.039 mg
TOP 85%
0.17 mg
TOP 87%
0.21 mg
TOP 88%
0.5 µg
TOP 89%
6.1 mg
TOP 90%
4 mg
TOP 92%

Vitamin chart - relative view

Vitamin C
7.4 mg
TOP 27%
19 µg
TOP 49%
Vitamin B6
0.12 mg
TOP 60%
Vitamin A
2 IU
TOP 73%
Vitamin B1
0.046 mg
TOP 74%
Vitamin K
0.4 µg
TOP 82%
Vitamin B5
0.123 mg
TOP 87%
Vitamin B2
0.027 mg
TOP 88%
Vitamin B3
0.116 mg
TOP 91%
Vitamin E
0.02 mg
TOP 93%
Vitamin B12
0 µg
TOP 100%
Vitamin D
0 µg
TOP 100%

All nutrients for Onion per 100g

Nutrient Value DV% In TOP % of foods Comparison
Calories 40kcal 2% 91% 1.2 times less than OrangeOrange
Protein 1.1g 3% 84% 2.6 times less than BroccoliBroccoli
Fats 0.1g 0% 93% 333.1 times less than Cheddar CheeseCheddar Cheese
Vitamin C 7.4mg 8% 27% 7.2 times less than LemonLemon
Net carbs 7.64g N/A 50% 7.1 times less than ChocolateChocolate
Carbs 9.34g 3% 50% 3 times less than RiceRice
Cholesterol 0mg 0% 100% N/AEgg
Vitamin D 0µg 0% 100% N/AEgg
Iron 0.21mg 3% 88% 12.4 times less than BeefBeef
Calcium 23mg 2% 50% 5.4 times less than MilkMilk
Potassium 146mg 4% 71% Equal to CucumberCucumber
Magnesium 10mg 2% 84% 14 times less than AlmondAlmond
Sugar 4.24g N/A 50% 2.1 times less than Coca-ColaCoca-Cola
Fiber 1.7g 7% 40% 1.4 times less than OrangeOrange
Copper 0.04mg 4% 85% 3.6 times less than ShiitakeShiitake
Zinc 0.17mg 2% 87% 37.1 times less than BeefBeef
Starch 0g 0% 100% N/APotato
Phosphorus 29mg 4% 84% 6.3 times less than Chicken meatChicken meat
Sodium 4mg 0% 92% 122.5 times less than White BreadWhite Bread
Vitamin A 2IU 0% 73% 8353 times less than CarrotCarrot
Vitamin A RAE 0µg 0% 100%
Vitamin E 0.02mg 0% 93% 73 times less than KiwifruitKiwifruit
Selenium 0.5µg 1% 89%
Manganese 0.13mg 6% 58%
Vitamin B1 0.05mg 4% 74% 5.8 times less than Pea rawPea raw
Vitamin B2 0.03mg 2% 88% 4.8 times less than AvocadoAvocado
Vitamin B3 0.12mg 1% 91% 82.5 times less than Turkey meatTurkey meat
Vitamin B5 0.12mg 2% 87% 9.2 times less than Sunflower seedSunflower seed
Vitamin B6 0.12mg 9% 60% Equal to OatOat
Vitamin B12 0µg 0% 100% N/APork
Vitamin K 0.4µg 0% 82% 254 times less than BroccoliBroccoli
Folate 19µg 5% 49% 3.2 times less than Brussels sproutBrussels sprout
Trans Fat 0g N/A 100% N/AMargarine
Saturated Fat 0.04g 0% 87% 140.4 times less than BeefBeef
Monounsaturated Fat 0.01g N/A 91% 753.8 times less than AvocadoAvocado
Polyunsaturated fat 0.02g N/A 94% 2774.9 times less than WalnutWalnut
Tryptophan 0.01mg 0% 94% 21.8 times less than Chicken meatChicken meat
Threonine 0.02mg 0% 97% 34.3 times less than BeefBeef
Isoleucine 0.01mg 0% 97% 65.3 times less than Salmon rawSalmon raw
Leucine 0.03mg 0% 97% 97.2 times less than Tuna BluefinTuna Bluefin
Lysine 0.04mg 0% 96% 11.6 times less than TofuTofu
Methionine 0mg 0% 98% 48 times less than QuinoaQuinoa
Phenylalanine 0.03mg 0% 96% 26.7 times less than EggEgg
Valine 0.02mg 0% 97% 96.6 times less than Soybean rawSoybean raw
Histidine 0.01mg 0% 96% 53.5 times less than Turkey meatTurkey meat
Fructose 1.29g 2% 85% 4.6 times less than AppleApple
Omega-3 - EPA 0g N/A 100% N/ASalmon
Omega-3 - DHA 0g N/A 100% N/ASalmon
Omega-3 - DPA 0g N/A 100% N/ASalmon
Omega-6 - Eicosadienoic acid 0g N/A 100%

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Nutrition Facts
___servings per container
Serving Size ______________
Amount Per 100g
Calories 40
% Daily Value*
Total Fat 0g
Saturated Fat 0g
Trans Fat g
Cholesterol 0mg
Sodium 4mg
Total Carbohydrate 9g
Dietary Fiber 2g
Total Sugars g
Includes ? g Added Sugars
Protein 1g
Vitamin D 0mcg 0%

Calcium 23mg 2%

Iron 0mg 0%

Potassium 146mg 4%

The % Daily Value (DV) tells you how much a nutrient in a serving of food contributes to a daily diet. 2,000 calories a day is used for general nutrition advice.

Health checks

Low in Cholesterol
 ⓘ Dietary cholesterol is not associated with an increased risk of coronary heart disease in healthy individuals. However, dietary cholesterol is common in foods that are high in harmful saturated fats.
No Trans Fats
 ⓘ Trans fat consumption increases the risk of cardiovascular disease and mortality by negatively affecting blood lipid levels.
Low in Saturated Fats
 ⓘ Saturated fat intake can raise total cholesterol and LDL (low-density lipoprotein) levels, leading to an increased risk of atherosclerosis. Dietary guidelines recommend limiting saturated fats to under 10% of calories a day.
Low in Sodium
 ⓘ Increased sodium consumption leads to elevated blood pressure.
Low in Sugars
 ⓘ While the consumption of moderate amounts of added sugars is not detrimental to health, an excessive intake can increase the risk of obesity, and therefore, diabetes.

Onion nutrition infographic

Onion nutrition infographic
Infographic link


All the values for which the sources are not specified explicitly are taken from FDA’s Food Central. The exact link to the food presented on this page can be found below.


Data provided by should be considered and used as information only. Please consult your physician before beginning any diet.