It's about one-and-one-tenth times as long as a Cricket Pitch.
In other words, 21 meters is 1.0439 times the length of a Cricket Pitch, and the length of a Cricket Pitch is 0.9579460 times that amount.(per Marylebone Cricket Council / International Cricket Council Law #6)
The length of a cricket pitch, from one bowling crease to the other, is 20.11680 meters. The wickets at either end of the pitch stand 0.720 meters tall including the bails.
It's about one-and-one-tenth times as long as a Bowling Lane.
In other words, 21 meters is 1.0963 times the length of a Bowling Lane, and the length of a Bowling Lane is 0.912160 times that amount.(USBC specifications; tenpin; including pin deck)
According to the United States Bowling Congress specifications, a tenpin bowling lane should measure 19.156 m. In a Professional Bowling Association game, the lane must be lubricated by about 25 ml (0.85 fl. oz) of oil.
It's about three-fourths as long as Baseball base distances.
In other words, 21 meters is 0.765530 times the length of Baseball base distances, and the length of Baseball base distances is 1.30630 times that amount.(MLB Official Baseball Rules specification)
According to MLB Official Baseball Rules, the distance between baseball diamond bases is 27.432 m. While second and home base are located upon the corners of the 27.432 sq. m area created by the bases, first and third base are placed within that square, to better allow the umpires to judge whether a ball is fair or foul.
It's about one-and-two-fifths times as tall as The Hollywood Sign.
In other words, the height of The Hollywood Sign is 0.710 times 21 meters.(a.k.a. Hollywoodland Sign) (Mount Lee, Hollywood Hills, Santa Monica Mountains, California)
Each of the white letters in the Hollywood Sign measures 15 m tall. Built as an advertisement in 1923, the sign was intended to stand for only eighteen months.
It's about one-and-two-fifths times as long as a Semitrailer.
In other words, 21 meters is 1.4350 times the length of a Semitrailer, and the length of a Semitrailer is 0.69690 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Transportation (DOT), the maximum allowable length of a semitrailer pulled by a road tractor truck is 14.63 m (unless superseded by state law). These regulations also allow the vehicles to tow up to 36,000 kg in gross weight.
It's about one-and-three-fifths times as tall as a Brachiosaurus.
In other words, the height of a Brachiosaurus is 0.630 times 21 meters.(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 13 m. 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 one-and-nine-tenths times as tall as a Telephone Pole.
In other words, the height of a Telephone Pole is 0.530 times 21 meters.(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 11 m 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.