It's about 10,000 times as wide as a Strand of Spaghetti
In other words, 21 meters is 12,000 times the width of a Strand of Spaghetti, and the width of a Strand of Spaghetti is 0.000083 times that amount.(average; restaurant and supermarket applications) (based on FMA Omcan Italian Made TR50 Counter Top Pasta Machine Extruder 13317)
An average strand of restaurant-grade spaghetti measures 0.0017 meters in thickness. In 2010, a California Buca di Beppo set a world record by preparing a 13,780-lb bowl of spaghetti, served in a swimming pool.
It's about 15,000 times as long as a Grain of Sand
In other words, 21 meters is 16,800 times the length of a Grain of Sand, and the length of a Grain of Sand is 0.0000595 times that amount.(medium grain)
Composed mainly of quartz, mica, feldspar, or magnetite, a grain of sand measures an average of 0.00125 meters. In 2007, a team of seven in Myrtle Beach created the world's tallest sandcastle, which measured 15.10 m (49.55 ft) in height.
It's about one-twenty-thousandth as long as The Grand Canyon
In other words, 21 meters is 0.0000471 times the length of The Grand Canyon, and the length of The Grand Canyon is 21,200 times that amount.(a.k.a. Gran Cañón) (Arizona) (Colorado River miles measure)
The Grand Canyon has a total length of 446,000 meters along the course of the Colorado River at its bottom. Having opened in early 2007, the Grand Canyon Skywalk allows tourists to stand on a horseshoe-shaped glass walkway 1,100 m above the floor of Granite Gorge.
It's about one-sixty-five-thousandth as long as The Rhine
In other words, 21 meters is 0.0000159 times the length of The Rhine, and the length of The Rhine is 62,900 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 1,320,000 meters 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 one-one-hundred-thousandth as long as The Colorado River
In other words, 21 meters is 0.00000901 times the length of The Colorado River, and the length of The Colorado River is 111,000 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 2,330,000 meters in length. Along this length, the river descends from its source, approximately 2,750 m above sea level in the Rocky Mountains, to its mouth in the Gulf of California.
It's about one-one-hundred-fifty-thousandth as long as The Danube
In other words, 21 meters is 0.00000737 times the length of The Danube, and the length of The Danube is 136,000 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 2,850,000 meters 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 one-one-hundred-fifty-thousandth as long as The Oregon Trail
In other words, 21 meters is 0.00000602 times the length of The Oregon Trail, and the length of The Oregon Trail is 166,000 times that amount.(from Independence, Missouri to Oregon City, Oregon)
The historic Oregon Trail stretched 3,490,000 meters 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.