The term “bean” refers to the seeds of various plants within the Fabaceae family, a category of legumes cultivated globally for thousands of years. These dried seeds form a significant component of human diets, providing protein, fiber, and micronutrients. The sheer variety across the globe means that generalizing about a “typical” bean size is impossible. The dimensions and shape of these seeds vary widely, ranging from tiny, near-spherical grains to large, flat, kidney-shaped seeds. This comparison explores the distinct physical characteristics and typical dimensions of common dried bean varieties, moving from the smallest to the largest available types.
Measuring Bean Dimensions
Determining the size of a bean involves standardized technical measurements to ensure consistency in agricultural trade and processing. The most common metric is measuring the three linear dimensions: length (L), width (W), and thickness (T) of a dried seed, typically expressed in millimeters (mm). These measurements are usually taken using a digital micrometer on a random sample of 100 seeds to calculate an average diameter or size.
Another important metric for commercial grading is the “thousand kernel weight” (TKW) or the count of seeds per 100 grams. TKW provides a standardized measure of mass that correlates directly with volume and size. This method helps account for the variability that exists even within a single cultivar due to environmental and genetic factors. These measurements refer to the dry seed, which increases significantly in both mass and volume after hydration and cooking.
The Smallest Beans: Mung, Adzuki, and Other Minis
At the smaller end of the spectrum are beans like the Mung and Adzuki varieties, which are often closer in size to lentils than to larger common beans. The Mung bean (Vigna radiata) is notable for its small, nearly globular shape. These seeds generally measure between 3.5 mm and 5 mm in diameter.
Mung beans are commercially graded by diameter, with common specifications including sizes like 3.0 mm, 3.2 mm, 3.6 mm, and 4.0 mm. A typical dried Mung bean has an average length of around 4.9 mm, a width of 3.7 mm, and a thousand seed weight of approximately 35.6 grams. Their small size and low mass per seed place them firmly in the “mini” classification.
The Adzuki bean (Vigna angularis), widely utilized in East Asian cuisine, is slightly larger than the Mung bean but remains small. These subcylindrical beans generally measure between 5.0 mm and 9.1 mm in length, with a width ranging from 4.0 mm to 6.3 mm. Commercial Adzuki beans are often sorted at sizes like 4.0 mm, 4.5 mm, and 4.8 mm to meet quality standards. The thousand kernel weight ranges from 50 to 200 grams, distinguishing it from common, heavier beans.
The Common Middle Ground: Black, Pinto, and Kidney Beans
Moving up the size scale are the medium-sized beans most commonly found in North American and international markets, belonging to the Phaseolus vulgaris species. Black beans, also known as Black Turtle beans, are ovate and have a jet-black seed coat when dried. A typical dried Black bean has an average length of 9.7 mm and a width of 5.2 mm. Commercially, their size is often quantified by count, with approximately 500 to 550 individual pieces fitting into a 100-gram sample.
Pinto beans, characterized by their mottled brown and pink coloration, are oval-shaped and slightly larger than black beans. Their length typically measures around 1/2-inch, or approximately 12.7 mm. This size places the Pinto bean at the upper end of the medium range, providing a creamy texture when cooked.
The Kidney bean, named for its characteristic shape, is one of the longest in this middle category. A large Kidney bean can measure between 10 mm and 12 mm in diameter, while medium varieties fall between 8 mm and 10 mm. Their long, uniform shape means fewer beans are needed to achieve a certain mass, typically requiring 180 to 220 dried grains per 100 grams for the large size. This size profile requires a longer hydration period compared to smaller beans.
The Largest Varieties: Lima, Fava, and Gigantes
The largest dried beans significantly surpass the dimensions of common varieties, often having a flatter or broader shape. The Lima bean (Phaseolus lunatus), particularly the large “butter bean” type, is known for its size and pale, creamy color. The mature, dried seeds can range from 10 mm to 30 mm (1 to 3 cm) in length.
The Giant Peruvian Lima bean frequently measures about 1 inch (25.4 mm) long, with a noticeably flat profile. Commercial grading for canned Lima beans classifies a “Large” size as being greater than 15.1 mm in width. This size contributes to their savory flavor and meaty texture when cooked.
Fava beans (Vicia faba), also called broad beans, are another large variety, characterized by their flat, oval shape. Dried Fava beans can reach lengths ranging from approximately 16.6 mm up to nearly 29 mm. Their mass is very high, with only 45 to 55 podded beans weighing 500 grams.
The Gigantes bean, a Greek variety of the runner bean (Phaseolus coccineus), lives up to its name, meaning “gigantic.” These extra-large white beans are typically kidney-shaped and measure between 3/4-inch and 1-inch in length (19 mm to 25.4 mm). Their firm texture allows them to maintain their shape well, making them a popular ingredient in baked dishes.