Onions are classified into various size categories mainly by diameter and weight, serving different culinary and commercial purposes. The largest category is Super Colossal, with onions measuring 4.5 inches or more in diameter, weighing over 21 ounces, often used in food service and for making onion rings. Slightly smaller are Colossal onions, around 3.75 inches and weighing 16 to 21 ounces, suitable for large slices and commercial use. Jumbo or Large onions measure about 3 inches and up, weighing between 10 to 16 ounces, commonly used in general recipes and retail.

Medium onions range from 2 to 3.25 inches, weighing 7 to 12 ounces, ideal for home cooking and salads. Pre-Pack onions, sized between 1.75 and 3 inches and weighing 4 to 9 ounces, are packaged small portions for retail. Small onions, measuring 1 to 2.25 inches and weighing 3 to 5 ounces, are perfect for whole roasting or pickling. Boiler onions are slightly smaller, between 1 and 1.875 inches and weighing 3 to 4 ounces, mainly for boiling and pickling. The smallest size, Creamer or Pearl onions, are under 1 inch and weigh less than 3 ounces, often used for pickling and garnishing.

In India, grading sometimes focuses on weight, with Big or Extra Large onions over 150 grams often used for salads and hotels, Ideal or Medium onions around 100 grams each for retail, and Sambar or Baby onions under 50 grams commonly used in South Indian cooking.

Yellow, red, and white onions are available in all these sizes, typically packaged in mesh bags ranging from 2 to 50 pounds or sold loose in bulk. This size classification helps in meeting specific needs for cooking, retail, and export markets efficiently.