It's about 1,500,000 times as long as a Semitrailer
In other words, 21,000,000 ells is 1,641,000 times the length of a Semitrailer, and the length of a Semitrailer is 0.00000060940 times that amount.(a.k.a. semi-trailer truck, a.k.a. semi, a.k.a. tractor-trailer, a.k.a. truck and trailer, a.k.a. eighteen-wheeler, a.k.a. big rig, a.k.a. Mack truck, a.k.a. transport, a.k.a. lorry, a.k.a. artic; for box truck; United States Federal length limits)
According to the United States Department of Transportation (DOT), the maximum allowable length of a semitrailer pulled by a road tractor truck is 12.80 ells (unless superseded by state law). These regulations also allow the vehicles to tow up to 36,000 kg in gross weight.
It's about 2,000,000 times as tall as a Brachiosaurus
In other words, 21,000,000 ells is 1,800,000 times the height of a Brachiosaurus, and the height of a Brachiosaurus is 0.000000560 times that amount.(based on comparable bone measurements, height to head)
Dinosaurs in the genus Brachiosaurus had an estimated height (at the head with neck fully extended) of up to 11 ells. A resin cast of the first Brachiosaurus specimen, owned by the Field Museum in Chicago, is currently on display at the O'Hare International Airport.
It's about 2,000,000 times as tall as a Telephone Pole
In other words, 21,000,000 ells is 2,200,000 times the height of a Telephone Pole, and the height of a Telephone Pole is 0.000000450 times that amount.(a.k.a. Utility Pole, a.k.a Power Pole, a.k.a. Telegraph Pole, a.k.a. Telegraph Post, a.k.a. Hydro Pole) (exposed height; per Florida Public Service Commission average)
A standard telephone pole is 9.60 ells tall. Despite alternatives, most telephone poles in the US are made of wood — most commonly pine — and have a lifespan of 25 to 50 years, depending on climate and preservatives applied.
It's about 3,000,000 times as long as a London bus
In other words, 21,000,000 ells is 2,860,000 times the length of a London bus, and the length of a London bus is 0.000000350 times that amount.(Routemaster Double-Decker, RM standard specification)
The Routemaster Double-Decker buses, well-known as icons of London, measure 7.330 ells in length. The buses were said to be well-designed for travel in the London traffic, as they offered an open door for riders to board and exit even while the bus was moving at low speeds, and a full-time conductor to collect fares.
It's about 4,000,000 times as tall as a Giraffe
It's about 6,000,000 times as long as a Beetle (Volkswagen)
In other words, 21,000,000 ells is 5,885,000 times the length of a Beetle (Volkswagen), and the length of a Beetle (Volkswagen) is 0.00000016990 times that amount.(1964 model) (a.k.a. Volkswagen 1200, a.k.a. Käfer)
A 1964 Volkswagen Beetle measures 3.5690 ells. As the longest continuously-produced automobile design — in production for 75 years between 1938 and 2003 — the Beetle was voted the most fourth-most influential car of the twentieth century by the Global Automotive Elections Foundation.
It's about 10,000,000 times as tall as a Christmas Tree (artificial)
In other words, the height of a Christmas Tree (artificial) is 0.0000001000 times 21,000,000 ells.(artificial; average height)
The most common height of an artificial Christmas Tree is 2 ells. According to the most recent USDA Census of Agriculture, a total of 1,389.59 sq. km (343,374 acres) of Christmas Trees were farmed in the US in 2007.
To all those observing, Merry Christmas from The Measure of Things!