It's about one-six-hundred-thousandth as long as The Rhine
In other words, 21 hands is 0.000001620 times the length of The Rhine, and the length of The Rhine is 617,000 times that amount.(a.k.a. Rhein, a.k.a. Rijn, a.k.a. Rhin, a.k.a. Rain, a.k.a. Reno, a.k.a. Rhenus, a.k.a. Ryn) (from near Reichenau, Switzerland through Hoek van Holland, Rotterdam, Netherlands)
The Rhine river runs 13,000,000 hands in total length. The World War II Battle of Arnhem, as memorialized in the 1974 book and 1977 movie A Bridge Too Far, was the first of several attempts to capture key bridges across the Rhine, beginning with the Arnhem Bridge in the Netherlands.
It's about 0.0000009 times as long as The Colorado River
In other words, 21 hands is 0.0000009160 times the length of The Colorado River, and the length of The Colorado River is 1,090,000 times that amount.(a.k.a. Aha Kwahwat, a.k.a. Grand River, a.k.a. Tizon River, a.k.a. Tecon River, a.k.a. Tison River) (from Grand Lake, Colorado through the Gulf of California)
The Colorado River runs 22,900,000 hands in length. Along this length, the river descends from its source, approximately 27,100 hands above sea level in the Rocky Mountains, to its mouth in the Gulf of California.
It's about 1,000,000 times as long as an E. coli Bacterium
In other words, 21 hands is 1,100,000 times the length of an E. coli Bacterium, and the length of an E. coli Bacterium is 0.000000910 times that amount.(Escherichia coli) (rod-shaped configuration)
An rod-shaped E. coli bacterium measures about 0.0000200 hands in length. A staple of biology labs, E. coli can reproduce in as little as twenty minutes.
It's about 1,000,000 times as long as a Mitochondrion
In other words, 21 hands is 1,130,000 times the length of a Mitochondrion, and the length of a Mitochondrion is 0.0000008850 times that amount.(Eukaryotic; average)
A mitochondrion measures between 0.75 and 3 micrometers (Âµm). The mitochondrion is commonly referred to as the powerhouse of the cell, responsible for the generation of ATP. The size, shape, and distribution of mitochondria varies widely, with human liver cells each having 1,000 to 2,000 mitochondria.
It's about 0.0000008 times as long as The Danube
In other words, 21 hands is 0.0000007490 times the length of The Danube, and the length of The Danube is 1,340,000 times that amount.(a.k.a. Donau, a.k.a. Dunaj, a.k.a. Dunav, a.k.a. Duna, a.k.a. Дунав (Dunav), a.k.a. Dunărea, a.k.a. Дунáй (Dunay), a.k.a. Tuna) (from Breg Martinskapelle, Black Forest, Germany through the Danube Delta, Romania)
The Danube river runs 28,100,000 hands in total length. Intersecting Vienna, Austria; Bratislava, Slovakia; Budapest, Hungary; and Belgrade, Serbia, the Danube touches more capital cities than any other river.
It's about 0.0000006 times as long as The Oregon Trail
In other words, 21 hands is 0.0000006110 times the length of The Oregon Trail, and the length of The Oregon Trail is 1,640,000 times that amount.(from Independence, Missouri to Oregon City, Oregon)
The historic Oregon Trail stretched 34,400,000 hands across five (sometimes six) states in the western United States. In the early years of the Trail's existence, the trip was estimated to have taken an average of 160 days.
It's about 0.0000006 times as long as The Volga
In other words, 21 hands is 0.0000006040 times the length of The Volga, and the length of The Volga is 1,660,000 times that amount.(a.k.a. Волга, a.k.a. İdel (Идел), a.k.a. Атăл (Atăl), a.k.a. Edil, a.k.a. İdil, a.k.a. Рав (Rav)) (from the Valdai Hills, Tver Oblast, Russia through the Caspian Sea)
The largest river in Europe, the Volga river runs 34,700,000 hands in total length. World War II's Battle of Stalingrad between the Nazi Germany and the Soviet Union, which resulted in nearly two million casualties, was fought in part for control of the river.