How big is Coffee Bean? | Scale of the Universe

A coffee bean is the seed of the coffee plant. Beans grow in pairs inside a small fruit called a coffee cherry, and are dried, roasted and ground to make coffee. The roasted bean shown here is 1 centimeter (0.4 inches) long. In a large study, unroasted arabica beans averaged 9.6 millimeters long, 6.7 millimeters wide and 3.7 millimeters thick.

Size

The figures above come from a study of 150 kinds of arabica coffee grown side by side in Peru's national coffee collection. Their unroasted, or green, beans ranged from 7.9 to 13.0 millimeters long and from 5.9 to 8.2 millimeters wide. An average bean weighed 0.16 grams.

Coffee is graded partly by bean size, which is checked with perforated screens rather than rulers. The screens have round holes sized in sixty-fourths of an inch, and graders record what share of the beans a screen holds back. In Ethiopia's grading system, for example, more than 85 percent of a batch must be held back by screen 14, which has holes 14/64 inch (5.6 millimeters) across.

Bean shape also depends on the species. Arabica beans are flatter and longer, while beans of robusta, the other main coffee species, are smaller and rounder.

Size comparisons

Two coffee beans end to end are about as long as a U.S. penny is wide, 19 millimeters (0.75 inches).
A coffee bean is about as long as an average cell of Thiomargarita magnifica, the giant bacterium described in 2022, which averages more than 9 millimeters.
A coffee cherry is about 1.6 times as long as the bean it holds, averaging 15.5 millimeters in the Peruvian study.
A kilogram of green coffee holds roughly 6,300 beans, or about 2,800 per pound, based on the average weight above.
An average coffee tree yields about 2 pounds (0.9 kilograms) of green beans a year, or roughly 5,700 beans.

From cherry to bean

A coffee tree begins bearing cherries three to four years after planting. Ripe cherries turn deep red or purple. Under the thin skin is a sweet, juicy pulp, and inside that each bean is wrapped in a thin layer called the parchment and a silver skin. In the Peruvian study, a bean still in its parchment averaged 12 millimeters long, 2.4 millimeters longer than the bare bean.

Most cherries hold two beans. In about 5 percent of the world's coffee, a cherry holds only one bean, called a peaberry. Farmers remove the skin and pulp either by drying whole cherries in the sun and then hulling them, or by stripping the pulp first and drying the beans afterward.

Arabica, robusta and roasting

Two species supply almost all the coffee people drink. Arabica made up about 57 percent of world production and robusta about 43 percent, according to the International Coffee Organization's Coffee Market Report of August 2026. Robusta beans contain 50–60 percent more caffeine than arabica.

Green beans are roasted in machines that keep them moving so they do not burn. When the inside of a bean reaches about 400 °F (200 °C), it begins to turn brown. A fragrant oil inside the bean, called caffeol, starts to come out, producing coffee's familiar flavor and smell.